Viewfinder Magnifier

I have a Nikon D3500 with an optical viewfinder as well as the normal liveview on the back of the camera. I'm nearsighted and wear contacts and as I'm rapidly approaching 40, I have noticed my eyes aren't quite as good as they used to be. I try to use liveview as much as possible but if I can't due to bright sunlight I use the viewfinder but I have noticed that I have trouble using the viewfinder with autofocus. Yesterday I was out on a nature walk and spotted 2 adorable raccoons playing/hunting in a small pond. I shot quite a few photos using autofocus, choosing the focus points that were near the raccoons to insure they were in focus. Unfortunately, when I got home and looked at the photos on my computer, a lot of the time they raccoons were out of focus. There was one area in one of the photos where the tree right in front of them was perfectly focused. So I know the camera is focusing but I think the problem is that my eyes are having trouble telling what is in focus in the viewfinder. If the situation is right and I'm able to use manual focus then I do but sometimes I'd like to be able to use autofocus with the viewfinder if I can't use manual focus or liveview. My question is, has anyone used a viewfinder magnifier? If you have, what brand did you use and did you find it helped? Some of them are fairly expensive so I don't want to spend a ton of money on something that won't work. Or did you forgo the magnifier and just use a pair of reading glasses? I appreciate whatever thoughts and opinions you might have. Thanks!

meganhaderphotography wrote: I think the problem is that my eyes are having trouble telling what is in focus in the viewfinder.

May I suggest that a magnifier would be of no help, really?
Adopting the BBF strategy and the appropriate shooting
method may be your needed solution.

I do like to use BBF but my problem is that I have trouble telling what is in focus in the first photo to continue to use BBF. I think I'm going to have to practice more and see if there is another way to be able to tell what's in focus in the scene when I have to use the viewfinder and autofocus.

I did not use any DX but I think there must be a focus
acquisition indicator in the viewfinder. Have a good time!