I have a few suggestions that should help:
- consider fitting lighter strings
(e.g. Ernie Ball Super Slinkies/Slinkies or similar 007/008) they are much easier to bend when you are starting out. They can be bent to extremes too.
- For acoustic guitar, suggest getting a set of strings with a lighter, non-wound G-string
. I used to use electric guitar strings.
- Use the third finger
to bend (not always, just usually) and then you can use the second &, possibly even the first, finger to help push up.
- Sometimes it makes sense to bend the G-string down
rather than up (I credit Brian Robertson
of Thin Lizzy for that tip, its on his "Still in Love with the Blues" video - learnt a lot of unusual, interesting stuff from that).
- for accuracy
in your bends (I think some call this "intonation"), if your ear is not yet good, try using one of those cheap $10-$20 Korg chromatic pocket tuners (love 'em, I have 2) to check you hit the right note.
Personally I wouldn't bother with exercise balls & hand strengtheners - just play a lot
and everything (ear, technique, strength, memory, knowledge) will improve naturally. If you really feel you must strengthen your hands try rock climbing or finger tip pull ups for effective hand/finger strengthening.