Sorry, I didn't know if you were doing it at home or in a gymnastics gym, hence the trampoline suggestion.
For backward rolls and backward rolls with straight arms, I find one the main keys is doing it with fingers turned in (as opposed to hands being parallel to each other or, even worse, turned out).
Here are some relatively easy, relatively safe skills that can be learned without much supervision with a bit of general fitness and coordination. Please remember that the human body isn't made to be in handstand (wrist issues are relatively common) and that no skill is 100% safe (you can always fall awkwardly, or onto something that isn't meant to be fallen on).
I am assuming you have more or less mastered the handstand already.
Handstands-like skills :
- obviously holding a handstand without moving the hands, which is actually hard.
- split handstand (like a regular handstand but with legs in split [or as close to a split as possible]) (I'm assuming you are female with an average flexibility for a woman). Unless your house is huge, maybe doing it outside is better than the living room
- double stag handstand, which is a split handstand but with both legs bend (which will probably look nicer than a split handstand and which I find a little bit easier),
- against a wall, shifting weight to one hand and raising the other above the floor. Be careful not to fall sideways.
- walking in handstand (quite easy, but very hard to do in a controlled, well-shaped handstand). Outdoors is probably better. If too easy, walk backward or, even harder, sideways.
Cartweel-like skills :
- regular cartweel
- bad side cartweel. Be properly warmed up for that.
- one-handed cartweel : with only the first hand (easier) or the second one (harder)
- cartweel, pause in the middle, get the legs together and go down like a regular handstand.
- "pop" cartweel (not sure of the english name for that) : like a cartweel but faster and with a flight phase after the hands touch the floor. Make sure you are properly warmed up. Might be a bit too challenging right now.
I'm sure there are others that I am forgetting right now.
Then, obviously, you could probably have fun in an adult gymnastics class, but those can be hard to find and/or expensive.