I’m looking for mental stimulation thing/toys for my 14 week old puppy

I have a mini golden doodle and he’s a really good dog, but obviously he has a lot of energy. We play with him a lot and he’s always playing with his toys, but I want to give him some toys that are more stimulating for his brain. I do give him lick mats, but I don’t wanna buy a bunch of crap that doesn’t work. If Everyone has any suggestions I would appreciate it. Thank you!