A "Belly Band" is adjustable and can be worn as high or low for your comfort as wanted. Most I have seen seem to be junk, but there are a few that offer good width (4-inches or more), have good retention (Velcro straps for weapon, magazines & other items), can be concealed under just a t-shirt and are maybe a better solution than the pocketed under-shirts.
I often use a BlueStone Safety brand one that comfortably carries most any pistol, 4 extra mags, a flashlight and a can of pepper spray. It conceals well under just a t-shirt, can be worn and accessed fairly easily when seated and is easy/quick to strap on or take off. This makes taking a firearm with me on quick trips to the store an easy decision and is comfortable to wear for long periods when other activities are done.
Getting under a shirt to access your firearm is not as easy/quick as a standard holster, but when concealment and comfort are high-priority, I find it hard to beat a belly band.