I agree with dd. I use those magnifier glasses all the time. I have a pair in #2 for the computer and #3 for the fine work. You can go and try them on for the strengths for your eyes. Test them out on some reading material in the store (i.e. a package) and take some small sewing piece with you and see if you can see the stitches ok.
Also get yourself some good eye drops like Systane Ultra. If you can't find them in the store you can probably get them online. They come recommended by my eye doctor.