I would have him cut down very short & keep him that way.
I see a lot of poodle x’s at work (bless you, my child for not calling him a schnoodle! :lol:). Many owners insist of leaving their coats longer because it is “cute”, but they do not see what these poor dogs have to go through to be dematted. It is a painful process. Even owners who attempt to keep their animals brushed out at home generally do not get down to the skin and miss areas that are especially prone to matting- the low belly, inner back legs, “arm pits”, between toes & around the butt. If I had my druthers, every dog that isn’t going in a show ring (which would be EVERY “schnoodle”, goldendoodle, cockapoo, etc…) would get cut close and come in every 5-6 weeks for a redo. “Cute” should not outweigh the animals comfort.
For grooming at home, burbank is correct- you need a comb as well. You can get softer slicker brushes; use the slicker all over to pull the coat apart & break up looser matts, then comb everything, all the way down to the skin. For stubborn matts, get a small matt breaker like this. Use it with a scooping motion to pull out the baddy. There are also longer bladed dematters like this that are designed for longer coats, but can be helpful for really nasty mats in very sensitive areas- gently pull the coat apart with your fingers at the skin until you find the “beginning” of the matt, tuck one blade of that into a few strands of coat there, and gently “shave” away at those hairs until they break. Repeat, always working away from the skin & holding the base of the matt to minimize pulling on sensitive skin.
If you keep him short, a quick once over with a softer slicker and combing a couple of times a week will be enough.