repleo Loc: Boston

A Sony A6000 with the Sony E 18-105mm F4.0 OSS combo only weighs 20 oz compared to approx 46 oz for your current combo . 18-105 should be plenty long enough for the subjects you mention. For a few dollars and a couple of ounces more you could go for one of the newer A6xxx series. Better still wait for the new Sony A7C full frame body at only 15 oz.
When you say camera shop in Manchester, I assume you mean Hunt's. Great people to deal with.

LWW Loc: Banana Republic of America

I have a D7200 and a friend just bought a D3500 and it is definitely less than one pound in weight without a lens and quite capable.

chrisg-optical Loc: New York, NY

Yep this is the way to go...

ELNikkor

Welcome to the forum, Tina! For minimal cost, you can get a D3xxx or D5xxx Nikon that is lightweight and will take the Nikon AF-P lenses, that are very light and sharp. Rather than have one-lens-does-all, like your 18-300, the D3xxx, or D5xxx series comes with a petite 18-55 kit lens that is very sharp and light-weight. For the longer shots, the 70-300 DX AF-P lens only weighs 14 ounces. Let us know what you decide...

CO

The D3xxx and D5xxx series Nikons have a pentamirror viewfinder. Your D7100 has superior pentaprism viewfinder. The glass prism inside gives a larger, slightly brighter view through the viewfinder.

Nikon eliminated the ultrasonic sensor cleaner in the D3400 and D3500. If you get one, get a filtered blower to clean the sensor.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

If you can't hold a D7100 with the 18-300 you may also have issues with a mirrorless.
I STRONGLY suggest you go to a camera store, explain to them your medical issues and the need for a smaller camera.
I would personally suggest a pocket camera, or a phone, you can't get much lighter.
My current favorite is the Sony HX-99. It has a 24-750 mm Zeiss zoom lens that gives me sharp 30X40 prints, has a built in Flash for great TTL fill flash outside and can shoot raw. And it is light. Below are a few examples of it's sharpness. And, it has a pop up viewfinder that is very nice to use. Good luck and keep on shooting until the end.

Toment Loc: FL, IL

Sony RX100 series
Whatever you do, be sure to try before you buy👍

dpullum Loc: Tampa Florida

Tina2 asks: " Unfortunately, due to a recent medical issue with my arms, the camera and lens are too heavy for me to use any more. I'm looking to buy a lighter camera. Does anyone have any suggestions?"
Unfortunately Tina, many do not read the words "too heavy" and buy a "lighter camera." You will end up with multi lenses in a bag and a tripod and such and all will be as i say, 40# of stuff for the closet shelf. You or I with minimal so called advance "point N shoot" equipment and minimal accessories will walk around with less than 2 pounds of camera 24/7 versitility and still have excellent image quality.

Cameras have built-in tri or mono-pods called fast shutter. Plus if you do not want or can't carry around a heavy camera... ridiculous to add to the burden.

There are a number of in pocket 24/7 cameras with one-inch sensors that do excellent photography. The prices drop when the models are replaced by the "updated" version. Some of these cameras have longer reaches than others that have other features such as articulating screens. Ponder your type of photography and select accordingly. Get the non-interchangeable lens type... the lenses are built in closeup to telephoto.

Filters? Yes, there are attachments for the cameras that allow the use of filters and add on lenses, 2x 10x and 0.50 wide-angle. These filters holders are either mechanical or magnetic... I chose the mechanical [threaded] adhesive attachment type; these support heaver or multi-threaded lenses or filters. Your lightweight bag is filled with photo magic.

If your grip is a problem, then adding a DIY plaster filled tennis ball to the bottom of the cameras adds inertia to the camera to steady it and when you grip with left-hand eagle claws 1/4"-20 tpi screw between your index and middle finger and camera against your right hand.. the team is steady as a rock. The example show needs a longer screw and additional rubber screw washer to allow your fingers to do the eagle claw grip and the camera is locked in position.
https://www.instructables.com/iSteadii-20-Image-Stabilizing-Unit/

Play the cards you have been dealt and make the best of it and enjoy photography. [me, soon 85]

https://www.bhphotovideo.com/explora/photography/buying-guide/cameras-with-1-inch-imaging-sensors#:~:text=%20Cameras%20with%201-Inch%20Imaging%20Sensors%20%201,sensors%3A%20two%20compacts%20and%20two%20superzooms...%20More%20

LWW Loc: Banana Republic of America

Actually, according to NIKON, the Z50 is heavier than the D3500 ... and the D3500 allows the OP to keep the glass they have.

camerapapi Loc: Miami, Fl.

"You may consider the 3000 or 5000 series Nikons. Much lighter and will accommodate the AF-S DX Nikkor lenses."

Bultaco Loc: Aiken, SC

Love common sense.

BuckeyeBilly Loc: St. Petersburg, FL

Try the D5600. Comparing it with your D7100, Nikon says that with the battery and card, the D7100 is 765g and the D5600 is 465g. That's close to a pound of weight which can be significant to the photographer. Now compare the two and see what you would gain or lose.

https://cameradecision.com/compare/Nikon-D5600-vs-Nikon-D7100

machia Loc: NJ

Perhaps go with a bridge camera?
I know people that have and are very happy.

mizzee Loc: Boston,Ma

I love my Olympus OMD e-m5 Mark III. I had a Nikon d7000 and a bunch of lenses. Loved the camera but hated the weight, so much so that I didn’t take it with me. I swapped all of it for the Olympus and have never looked back. I take it everywhere. It and two lenses fit comfortably in my Hobo bag with camera insert and it weighs less than my old Nikon with a 15-85 lens. The in-camera stabilization is hard to beat. I started with the m5 II, which is still around and selling for attractive price. My first lens was a 14-150 II — weather proof.

I don’t know how far away from Manchester you are but Hunt’s Photo is a great resource and they won’t try to up sell you something that isn’t right for you.

bikerguy

The Olympus OMD-EM10 Mark IV with the 14-150 mm. It is light and an excellent camera and lens and much lighter than the Nikon set up you currently use.