Alli has a foam pad and at first I was skeptical but gave it a go. Best money I ever spent!!!! Mine was a wintec back raiser pad but you can get front raisers and just a plain and simple packpad. You can trim the foam, and it doesn't slip while under saddle (with leather anyhow)
It is quite thick which I thought would interfere with the fit but it seems to only help, not hinder our saddle. Alli is comfortable under it and I can't tell the difference feel wise!
I would go foam all the way