Hey! Yes that’s a tricky style to play against for sure and not easy to find the right tactics. I would say in this situation variation is key, so keeping them guessing with sometimes playing topspins, sometimes slower drives, sometimes pushes. This means they can’t get into a rhythm or routine and also forces them to make a lot of decisions.
The same when you serve, it’s important to change often, so like you said long backspin is good sometimes, also the sidespin you mentioned, short float into the middle or forehand can be another effective one.
If you really give them a slow ball and can keep it low, with the anti it’s hard to generate a lot of speed, so this can be good sometimes too, trying to be patiand slow the game down until you can get a chance to play a strong topspin. Then the last thing to focus on is when you do play your stronger attacks really try to find the middle/elbow of the opponent. This makes it much harder for them to control back and return as they have to move into position.
Let us know if you have any questions on that and how you get on! 🙂