Hello Sharon. I too have very little eyesight, and I use an S970, that operates the same way as the S975.
Before you make any decision regarding your Genos, note that if you have the newest firmware update of it, you have voice assistance. It has to be activated, and you may need help to go into the menu and do that. When activated, the voice assistance will function like VoiceOver on the iPhone. BUT, since I do not have a Genos I cannot say how good it is. Hopefully it will be developed by Yamaha to become even better in later updates.
The Tyros and PSR keyboard have no such features. BUT, they have buttons, and can therefore be navigated without using the screen. I know this, because this was how I operated my old keyboard. I never fiddled with the menu, just took it out of its box, found out what the buttons did and listened to the internal styles. Than I made myself a papar (with BIG letters, where I wrote down what buttons to press to get this and that style.
All this is possible on all Tyros and PSRs. The Tyros 4 is a much bigger instrument, and may have better buttons. But if portabillity is important to you, then choose a PSR model. The buttons are smaller, but distinct, and easy to find when you get the hang of it. BUT; DO NOT DO ANYTINIG BEFORE YOU HAVE TESTED OUT THE VOICE ASSISTANCE ON GENOS!!
Please let me know how this turns out.
Good luck! I know what you are struggling with!