Seated AIWB is extremely comfortable for me with a HK P2000 or G19 sized gun. I've driven all day in this arrangment without any problems. I'm 5'10" 180". I might have problems with a pistol with a longer barrel.
I generally prefer a belt that is not super stiff. JM Custom Kydex or Dark Star Gear are my go-to holsters. Ride height and cant adjustment is good. If I carry a spare mag, it's usually in my pocket.
FWIW I find the Side-car holsters horribly uncomfortable.