Ah....finally someone who sees what I see as a problem with all this topspin. It's all too readable. I'm fairly old-school (ok, well, OLD) myself and hit the ball fairly flat. I eat up playing topsinners because the ball indeed sits up. When I do run across a "mirror" (someone who hits it flat or even with slice), I have to really concentrate. The key, I've found, is in the footwork and legwork. Stay on the balls of your feet more and be ready to respond (forward, backward or sideways). But even more importantly, IMO, you've got to bend those knees, really get down for those shots...if you want to keep your swing/arm motion the same/similar. Almost feels a bit like playing a racquetball game (which I loved!).
Good luck and
for playing a guy with a different style. It'll improve your game.