We were sent some Little Wonders Small Safari Non Slip Bath Splat Mats. The idea behind these is that you stick them on the bottom of the bath and then sit your child/baby on them so that they don't slip over.
I think they are a great idea. Unfortunately for us, they didn't work so well in practice. Purely because my son kept pulling them off the bottom of the bath to stick on the side of the bath. He doesn't want to get in the bath without them now - even if it is just to play with them!
If you have a child who could leave them alone then they would be brilliant. In fact, when we used them solely with my daughter (11 mths) she didn't pull them off and sat very safely. So maybe they are better for younger children.
They do stop the child slipping, they stick down well and wouldn't be easily removed by a small child. Also, you could buy a couple of packs for greater coverage of the bath!
You can buy these here.