I have this same issue.

For reference, I'm twenty-eight years old right now. I had my first premolars removed in my maxilla when I was about eleven years old. My canines were up in my gums, and they had to make room for them to come down when I got braces. So ever since them, my maxilla has been smaller than normal. Good news is that the removal of my first premolars allowed my wisdoms to grow in without a fuss.

Anyway, my tongue pretty much touches all my teeth when I mew, but I smash my tongue up to my soft palette to get it up there, and several times throughout the day I'll press my tongue against those teeth for maybe three to five minutes at a time. I also chew Falim gum and press that against my soft pallette as well.