Just resurrecting this thread as I'm considering buying a whirlpool bath when we refit our bathroom.
I've had a bubble mat like the one mentioned above for a few years, but they no longer make replacement mats.

Also I've found that the suckers come off the mats fairly easily and that the mats can gunk up quite fast too even if you rinse them thoroughly. So, time to get something more permanent.
I'm planning to go to a show room and quiz the sales people but was just wondering if anyone who already has one has any comments on what I should look for. Thanks.