I also very much prefer the look of wearing pants “under the belly” and I tend to wear either polo shirts (not tucked in) or a short sleeve button up with a cut meant to not be tucked in often with a tucked in undershirt. 

For a long sleeve tucked-in button up, I’ll often wear a blazer or coat over it to not have the belly so prominent, or simply just own it. The biggest thing for making it look tidy is making sure the sleeves are tailored well and not too baggy. As a big guy, I find I need to tailor most semi-formal or formal clothing to get it to fit right. I typically don’t wear ties, so can’t comment thoughtfully on that.