
You've got good brushes already - the slicker especially, I recently recommended one to a TT owner whose dog is always very matted, he turned up for his latest groom today almost knot-free!
My tip would be to use a double comb as well - once you've given the coat a good brush over, use the wide tooth side to run through the fur and check for fair sized knots (carefully of course!) and then the fine tooth side to find any last stragglers, if there are any. It proved invaluable with that TT today - I thought I had all the knots out, but on going through with the comb I found a few that bathing him would've made harder to remove. Make sure you brush under the armpits and bum, a lot of people forget these spots - also under the ears.
Sounds like you're doing a good job - keep it up!