I vote for a professional groomer as well.

I have a nice set of clippers, do all the bichons myself and after 5 or 6 times take them to the groomers to get them back in shape, fix whatever I haven't been doing correctly.

Vita is a long haired cat and now that she is older, she is matting regularly. I have tried everything I have learned ont he dogs; to no avail. I have had her in to the groomer's twice now, something we never did in her first 9.5 years!

The best idea I can give (and so far I can't seem to do it!) is get her cleaned up at the groomer and then brush her regularly ( daily? morning and evening?) to prevent the mats returning. Easier said than done.

Good luck!