I hate soft beds and silky quilt covers are only any good if they are cotton underneath, otherwise you can't get a good hold. A firmer bed allows you to get a little closer if you know what I mean *winks* and helps the rhythm, whereas a soft bed absorbs too much and makes it all wishy washy and frustrating. Well that is what I think anyway. I much prefer a good hard stiff grip
It's all very scientific really, with shock absorbing, friction, energy wastage etc.