The best toy I've ever found for my whippets was not actually found by me, but by my whippets!
We were walking the two whippets at a high school where they apparently play LaCrosse.
Our boy dog came back with a LaCrosse ball and carried it all the way home.
They don't bounce very well, so if your whippet loves the big bounce, never mind. But they are made of some very firm rubber that my whippets have not been able to crack, chip, or chew through, yet it's soft enough and small enough for them to chew on. And not too small.
The ball (now 2 balls) they found have been played with constantly for about 6 months now!