Here's an article you might find helpful on selecting a quality probiotic.
http://www.supplementspot.com/aguidetoqualityprobiotics.html
If you do a search, you'll see the top brands members here have recommended. This topic comes up alot.
As to dose, you're going to want to start off slowly and work your way up to the manufacturer's recommended dose. Anyone with IBD is going to need billions of colony forming units per day.
Although Mercola is touting his own probiotic formula, you may find this education video informative. He gives alot of general information before getting into the specifics of his formula:
http://products.mercola.com/probiotics/