i've been having the same problems. i picked up Kung lao and buzz saw is too much fun. B2/B22 low hat is a good start to basic low/overhead mix ups and F23 is a good low starter, although on block F23 is full combo punished. You have to condition a standing opponent to block F21 which is safe on block if you cancel into teleport or low hat, so when they see F2 start, they won't change block stance.
you can make strings somewhat safe by cancelling into teleport and doing tele-3 or tele-4. Teleport 4 is +19 on -block- but doesn't allow for combos after it hits(hard knockdown)
Scorpion is surprisingly fun with mixups, but you said you wouldn't want to play him(i don't blame you, i'm the same with picking mycharacters.)
Raiden has overhead and low starters and gets great damage in the corner. His Thunder God variation is gdlk for building meter and chip damage.
Cassie Cage has high/low mixups as well and has an amazing punisher with B12-flip kick, as it's a fast advancing normal. Jax is similar with F2 i believe the button is.
if you look into it, a lot of characters have good overhead/low mixup games and a good handful have really great vortex games that work off of pure 50/50 or even 33/33/33 options. Erron Black also comes to mind. The fortunate thing is that all the characters really feel viable, and it's early enough in the games life that you can pick anyone and learn new stuff and bring tech to the table. It's up to you who like design wise. i recommend picking two different characters you like the look of and going into training mode and checking out their strings. You can swap control to P2 side and control the dummy and look up his move list as well, so you can maximize your time testing out what you like and don't like.
