I think the cabbage leaves are to relieve engorgement(?) rather than sore nipples as such?
rrt, I think the best thing you can do is to let your dw feed whenever baby squeaks - so get her lots of cups of tea, stay in bed all day with the baby etc!!! Also, feed feed feed through the night when the prolactin hormone is greatest.
The feeling of full/empty is quite misleading, don't assume because she doesn't 'feel full' that there isn't any milk there.
I had supply problems with ds1 and ds2 - with ds1 I never got off the formula supplements, and it did work well, I b/fed him up to 13 months, but I did feel depressed about it. In between the boys, I had dd who had no problems, which gave me the confidence with ds2 to persevere - he had a small supplement for about a week.
As people have said, just feed feed feed to increase supply - start by dropping one bottle at a time. Don't be afraid to switch sides as well - I found that helped.
What really turned things around with ds2 was topping up with EBM - this is a bit contraversial on here, as it is a PITA - I would express on one side prior to a feed (and generally get about 2oz), express a tiny bit of the other side (0.5-1oz) - supposedly to increase the 'hindmilk' (again a contentious point - if I understand tiktok correctly it is all the same milk, but as the breast is emptier, the milk is creamier), then feed off the side which had only had a little expressed off, switch to the other side, switch again, switch again then top up with the EBM. This would take half an hour or so, I would then put him down to sleep, wash the breast pump (I had a Medela electric one which I found far better than the hand one), sterilise it all, by which time it was nearly time to feed again.
I was feeding regimentally every 2 hours (beginning of feed to beginning of feed). If you tried something like this, what would have really helped me would have been my dh doing the 'in between' bits, so I could sleep, because as ds2 was my third, I was shattered!
I'm not pretending to be an expert on this, but it did work with ds2, along with lots of advice from tiktok, hunker etc. And once I established a routine that was easier in a way.
I said it earlier, but I do think the most important thing at this stage is not to let him go too long between feeds, especially at night. I got my dh to bring me a cup of tea for night feeds which really made a difference psychologically!!!! Hope things sort out.