It's love, plain and simple. I have two shelter cats and they just KNOW to love the human(s) that rescued them. You have one happy, well adjusted kitty on your hands.
The jumping on the back of the couch and the toy(s) in the mouth could mean that he wants play time. Do you know if he's been around other cats? He may be looking at you to play with him. A cat under two can still act like a little kitten and be crazy and silly and may still need lots of playtime. He's elected YOU as his buddy and that's the end of it.
Following you is again, love. My cat does this, too. Everywhere I go, there he is! He knows you're his savior; you rescued him after months of being all alone in a shelter and he's a grateful little fluffy butt. My cat was up for adoption for 7 months before my husband and I rescued him, the poor thing. We get purrs, head bunts, kitty kisses, and he kneads us all the time.
Your cat knows he has a good human who spoils him, a warm place to live, lots of food and water, and a human that loves him unconditionally. All these little things he does for you are a cat's way of showing you gratitude.