Yes the full body suit would be too warm in the day to wear without air conditioning.
Booties and mittens are worn to prevent babies from scratching themselves so my son still wears them in non-a/c places.
Usually in the day my son will be in short-sleeve or sleeveless rompers. Sometimes, like what you described, t-shirt + diapers + shorts.
As a general rule of thumb, wear what you feel you would feel comfortable in. If there is no air conditioning, I doubt you would feel good wearing a long sleeved footed romper.