My opinion....you really need a belt...you can get by with "hanging" it in your sweat pants or "jammie" bottoms when you need your hands free for a moment.

You might try a narrow web belt under your sweat pants. You could even attach a Tough Strip reload pouch under your sweat pants.

I used to carry a model 38 using the hip grip as pictured with the paddle under the belt. I kept the gun covered w/ a T shirt or sweatshirt. My job required some mild athleticism: jumping, climbing, crawliing. The gun never fell out of place. While "river ratting" with some friends I actually fell out of a sweet gum tree into a river, hitting and grappling for tree limbs on the way down....the revolver was still where it was supposed to be after swimming to the bank.

Some one from this sight informed me of a "lip grip" manufactured from laminated wood that is very attractive.

Custom Pistol Grips and Kits - CollinsCraftGrips