Tummy tuck or mini tummy tuck to fix scar and overhang? (photo)

It looks like a mini tummy tuck will suffice, as long as you are not expecting any change in the upper abdomen. If you are not able to correct the muscle separation with exercise (most of the time this doesn't because there is no exercise that pulls the muscles toward each other), then consider a mini tummy tuck with umbilical float. That would allow for a full muscle repair.

Based off your photos - (without a physical exam) - it does not seem like you have much of a diastasis recti either (great physique for being post-partum), but I do agree with you 100% - core exercises (pilates) until your core is strengthened again is very much needed post-partum.
Looking at the scar and your lower abdomen - you can address this situation with some liposuction with scar revision, or do a mini TT in the future depending on how your lower abdomen has healed and how your core muscles have been strengthened. I think the key here is to make sure the scar heals without tension so you do not develop a hypertrophic scar (potential keloid) again. And remember if you have developed thickened scars / keloids once, chances of that happening again in the future is more likely than less.