How difficult would it be to have my tubes tied?

It's harder than you think. There's a lot of resistance to sterilizing younger people. I had a vasectomy when I was in my 30s because I was done having children and my wife and I didn't want to have to keep using condoms or worrying about it, and I still had to deal with a doctor asking me if I was "sure." Yeah, I'm sure, or I wouldn't be here. That's like a grocery store clerk asking if I really want that head of lettuce in my shopping cart. Not only that, the copay was ten times what it was for any other procedure, including the entire cost when my kid was born.