It's a matter of personal preference both android or iPhone will work, but for me I am using my iPad mini. Phone is just to small for me to use as FPV monitor I think iPad mini for me is just the right size and battery last long. So far I'm loving it... good luck!
Just a matter of what you want, I use a Samsung Galaxy Tab4 7" , it seemed to work when I had the few chances to use it. Big but not to big small but not to small.
Size and brightness are the 2 most important! my Droid Razr Max is bright but small, my droid tablet I bought for $50 is big but not bright. I happen to win an ipad mini and VIOLA! size AND brightness! Nirvana!
I got some cheap magnification glasses from Amazon +1.00, +1.25 up to +4.00 - 3 pairs for just over 10 euros. Wear them down your nose slightly to view your android and look over to see you copter. Don't think I'll bother with a 7 inch tablet now.
Also handy for fine work on electrics etc.
Jobs a good un.
If you have a Dollar Store, they have readers for 1.00. Just get the thickest frames you can get as they will last longer. I have about 4 pair ($4.00 worth!) of super magnification for use with the iPhone when flying, soldering, etc.
Just to let you know that your eyes are unlikely to be identical sight-wise. If you wear a pair of cheapo specs/magnifiers regularly, it may well have a deleterious effect on one or both your eyes' lens capabilities, reducing your sight faster than normal age-related factors. Best get your eyes measured and have a proper pair of specs made for your particular sight deviation. You'll see better too.