Hydrogel breast discs inside your breast pads help with the nipple not being so painful between feeds and lasinoh can help too.
You can use formula or ebm in the supplemental nursing line, probably better than giving bottles as there is the chance that bub will prefer the bottle as it is easier, and then there goes your bf'ing relationship. But it means your breasts don't get a break, which is so hard when things are painful.
I would try to balance the extra expressing with getting yourself some rest too, as if you're exhausted it is more difficult for you to produce much milk.
The 10-20ml amounts you are expressing aren't that bad, when I was expressing the damaged side (so not feeding off that side) I would get about 40ml and DS would feed off one side then have the 40ml and do that no more often than 3hrly and his weight gain has been fine.
My LC also got me to feed lying down so the painful/ damaged part of the nipple wasn't constantly being hurt again.
It is a hard road, especially when you dread every feed for the pain and so very stressful if you worry that they aren't getting enough milk. I had a similar problem with DS1 (minus the TT) and managed to get through it with him too, but that didn't mean I haven't contemplated giving DS2 formula (I even made him a bottle once, but he settled before I could get it to him)
Sorry that is a bit if a ramble, I am really feeling for you and wish I could do more to help!