I'm a groomer, and I'd advise the metal comb you prob already have, although the one I swear by is quite small, with medium and fine teeth - no handle or anything just a plain metal comb. You can see a pic of it on my website in my profile. As Candyshandy said, comb against the lay of the fur right down to the roots. Any knots, you could try teasing out with your fingers and then combing, the little comb can also be used to tease the knots out too - just use the tip of the end tooth to gently tease through the mat.
If the knots are just underneath - tummy and inside back legs, you could see if theres a good groomer near you who does cats and maybe have the underneath shaved, if thats going to be a problem area, as it won't show - unless like my Persians yours like to lie on their backs!
The best method of keepin coats knot free is bathing and blow drying - it gets rid of all the dead fur (which is what causes the mats - by binding to the still growing fur) in one go - and the best bit - is that you don't need to do hardly any grooming in between baths because they don't knot up - honest it works! I've had persians for 10 yrs now and been grooming other peoples too for 6 yrs. The breeder of some of my Persians showed me how to do it initially.
I've got colourpoints but I find their coats easier to groom than the solid colours - I've got a solid red boy Joe - the namesake for my grooming business Scruffy Joes! and his coat can be quite woolly.
