The way I sling my rifle causes the extended charging handle to dig into my gut, and this becomes extremely painful after about 30 minutes. The extended charging handle is currently on the left side of the gun, I would like to be on the right side (ejection side) only.

Even better would be making it side charger via a knob & upper machining.

Why couldn't you get an extension on the right hand side of the charging handle? Take the left side extension off and put one on the right. Put a standard latch on the left side, in case you need it. They make charging handles with dual extensions on each side, so you could just take off the one on the left. I have had your same issue where you feel the charging handle digging in.

Just like this:

That’s what I was looking for, but my search returned either extension on the left or on both sides.

I would think you could purchase the right side extension, and put it on yourself. I have added 2 extensions to my charging handles, and it's not hard to do. You just need the correct size punch to remove the retaining pin to uninstall and install the new one. But, I'm not sure if there is a recess on the right side of your upper for the right side extension to catch on to.

If I'm not mistaking most milspec charging handles dont have the hole for the roll pin on the right side. Youd have to buy an ambi charging handle then take milspec extension off your original one and replace the extended one on left side on the ambi.

Or just buy an ambi raptor charging handle it's all I run and they're more tapered than the gun fighter extensions and dont dig into stomach when sling across your chest.

https://radianweapons.com/accessories/charging-handles/raptor-charging-handle

What I just bought for the last AR-15

The reviews said "if this is your first one, you might as well buy one for ever AR you have". That's correct, I should have bought 3 instead of 1.