Oh I'm so sorry to hear your story, it sounds very familiar unfortunately. My DS is 10 weeks old and I could have written your exact same post.
DS had his posterior TT snipped at 3 weeks. The lactation consultant said it would take 2-3 weeks to improve, but there was no improvement and at 4 weeks post-snip we found out it had reattached. We had bumbled along with ebf until then with a mixture of good and bad feeds, but around that time feeding got worse. DS would fight the breast or just suck a couple of time and then sit there and do nothing/fall asleep. I think this happened because my supply was starting to regulate, because previously I had oversupply so he didn't have to do much to get the milk.
It became counterproductive to try and fight to get him on the breast as he was developing an aversion, plus I needed to get some milk into him. So I started expressing round the clock, and he was mainly either finger fed or bottle fed during the day, and breastfed during the night (strangely he doesn't fight the breast at night!).
We are now 10 days out from the second snip which was done by laser. Sometimes I can manage to get him to latch on and feed, but mostly he refuses, or latches but then starts fussing. Some things that do sometimes help him to latch are to have him suck on my finger or a dummy, and then quickly put him on the breast, to catch him when he is just waking up from a nap and sleepy, or to put some white noise on in the background.
At the moment I am expressing about 6 times a day after feeds (whether it is breast or bottle) to try and maintain my milk supply. I had the same problem that you did last week when I tried to ebf and didn't express at all for a couple of days and my supply totally dropped - I could tell because I only got 10 mL from one breast when I expressed in the morning, compared to about 100 mL normally!
Are you doing any suck retraining exercises? DS needs to learn how to reuse his tongue so a handful of times a day I have him suck on my finger and pull his jaw forward at the same time with the other hand to get him to suck properly. Also running your finger along his bottom gum from side to side to encourage his tongue to move properly is supposed to be important.
Have you checked that the TT has not reattached? It seems to be fairly common.
I can totally understand why you are thinking of moving to FF feeding, as I am in the exact same position. My plan is to give DS about another week, and then I will stop expressing, or limit it to once or twice per day. We are also pretty housebound and I would like to get out more as I've given it a good shot now and I'm ready to move on. I will still bf at night as long as he will accept it and I have milk, and I'll probably keep doing the suck retraining exercises on the off-chance that he improves and I can give bf another shot. The GP is worried that I have/might develop PND, but she has said she has not concerns about moving DS onto formula. I found it useful to hear an objective view as it puts things into perspective.
Good luck whatever you decide. I totally get where you are coming from, it is so so hard 