In my own case, I am also dealing with eyesight. It happens as we age, ;/
I have been using a 27" 1080P monitor for years. It's contrast is a bit crappy due to the size, and of course going larger makes it worse. I opted to stay 27" but move up to 2K and am hoping that I can make adjustments to scaling and text size to make work easier without glasses on (that I don't need for not reading). I tend to agree in large part with some of the argument made above about said.
Let's hope we can alleviate some eye strain.
Contrast has little to do with size or resolution. It's most impacted by the type of display and the panel design.
CRT, Plasma and Oled are capable of significantly better contrast than LCD because they light pixels individually and the phosphor glow is the actual light source. One group of pixels can be brightly lit while the ones next to it can be left off creating the potential for excellent real world contrast.
LCD uses backlights instead of lighting phosphor pixels individually. This makes it impossible to produce super bright areas next to pitch black ones without light bleeding over, blurring edges and washing out the image. Later models have improved blacks by adding dark filters but they're still inferior.
I don't believe any of the above will help with age-related eye strain though. Going up in resolution usually makes text smaller unless you change the font size. I struggle to read text on my 77" 4K Oled because it's so small. I had no issues on the similar size 1080p display I used before.
If you can't read text, step 1 is increase the font size in Windows. If that doesn't help, make an appointment at the optician to get stronger glasses.
If the eye strain is in the form of headaches from staring at the screen, try turning down the brightness and / or using Window's high contrast mode. This basically flips the colors so you're reading white text over a black background instead of the usual black on white.
If you park the eye-strain issue and say you simply want to treat yourself to a nicer monitor (there nothing wrong with that). Moving to a 1080p (or 4k ) 120hz will produce better results IMO than going from 1080p 60hz to 1440p 60hz. This applies equally to text reading applications as it does to graphics.
If you want to see for yourself the effect of raising the framerate, try lowering it on your current monitor from 1080p 60hz to 1080p 30hz. Then try reading text. You'll notice immediately that it's blurry by comparison. You'll get a similar improvement going from 60hz to 120hz.
Above all, go see a monitor in person before buying if possible. For all the general advice you'll get here, each monitor is different and there's only one way to tell what works best for you....