I agree with the posters above who mentioned switching to a comb. Most brushes on the market are going to be too rough on a cat's sensitive skin. Combs work wonderfully to pull out dead undercoat and small mats.
A trip to the groomer is also another solution. A professional groom does not automatically mean a lion cut. I offer 3 options for clients when they come in with long-haired cats:
1) A bath and blow dry (includes nail trim, ear cleaning and sanitary shave) every 6-8 weeks. This keeps them in beautiful full coat with no matting, no excess shedding and requiring very little at-home grooming. *Some very full coats, especially if they are dilute colors may need more frequent grooms - the more cottony the hair, the more easily they mat. Persians in full show coats are usually groomed weekly.
2) A comb clip (also called a teddy clip/kitten clip) every 8-10 weeks. This takes off about half of the hair (sometimes more, sometimes less). This still leaves them fluffy but not as high maintenance as a full coat - and also with minimal work at home.
3) A lion cut every 3-4 months. Shorter coats mean less maintenance, this is a good option for busy households or those on a stricter budget.
Cat mats mainly form because of two things: shedding/dead coat and greasy skin. All cats are greasy (the only exception may be from a medical condition). When dead coat tries to shed out, it can "stick" to live coat from the grease. Most coat sheds, gets stuck, and then more coat, etc. The greasy, dead coat compact together (think of a brillo pad) and that's why most cat matting is clumpy but can sometimes come out easily with a comb. A bath and blow dry can eliminate the two causes of cat matting. A bath with degreasing shampoo removes the grease, and the blow dry and comb out remove any dead hair.
Combing at home can help remove dead hair and while it can't remove greasy, it can more evenly disperse the natural oils in the coat so it is not as clumpy. The older cats get, the more oils they produce and the more likely they are to get matted. I recommend getting younger cats used to regular grooming appointments to avoid matting issues when they are older (since starting grooming geriatric cats for the first time can be very stressful, if they are already used to the schedule then it is not). I did 2 geriatric cats today at the salon. One comes in every year and has to be sedated since he is horribly matted, has paper-thin skin which makes it much harder and riskier to shaved, and is just a general grouch to the whole process. The other geriatric cat today comes in every 8 weeks for a bath and blow dry (no sedation). She has beautiful coat and does very well with the whole groom. She usually only has minimal matting that comes out during the blow dry (so no shaving, and no yanking matts out). These cats are 17 and 18, respectively. Hope this helps!