This is okay, if you maybe want to add a little height.  I wouldn't call it "firm".  We keep it in place thanks to our thick mattress pad & fitted sheet and the straps we bought to criss-cross under the mattress (otherwise it would slip). I would not recommend if you are looking firm support/relief for back issues. Average size man and slim woman roll into each other and find it hard to sleep. I don't see this staying on our bed for too long :(