Sorry OP I don't have much advice but wanted to give my sympathy, must have been so hard for you 🫂
Mine was 2nd centile and I think mild jaundice as we managed to escape the triple feeding. That must have been so tough.
Have you checked with the health visitor? I'm not sure about elastic nipples, I know it's good to get the right size flange so you don't hurt yourself.
Not sure how old your LO is, I found the haakaa really useful to collect some letdown while feeding on the other side, it felt like no more work really since I was already feeding. Built a milk stash that way and it meant when DH used that to feed our baby, I'd miss a feed or two and that meant I got more out of the pump.
Edit: just to add, I agree with PP, really important to feed or pump between (I heard 1 and 4am or 2 and 5am) so not to reduce your supply. I pumped between 6 weeks and 3 months and DH would take him for 4-5 hours at night so I could sleep. Depending when he took him, I'd set an alarm to wake up and pump during that key window.
Definitely recommend going to sleep as soon as baby is asleep - if you can get them down in a cot or hand them off in the evening - and getting a break then. Mine was in a bedtime routine from at least 3 months and I'd go to bed as soon as I got him down.
Lastly, it depends what you want and how you're coping. You've already been through the triple feeding. If you want to prioritise breastfeeding and maintaining supply, I'd ask for support with pumping effectively, are there any breastfeeding support groups in your area? I started cosleeping with LO once his circadian rhythm started to show, and after his first stretch of the night in the bassinet - DH would keep an eye on us with the monitor, while working downstairs. Still doing it and that actually felt more restful than waking up in the early hours to pump both sides with a manual pump, store the bag etc.
Sleep deprivation can really affect your mental health though and if you're really struggling then it's fine to give formula if that will help you be the best mum with some rest. I would never tell anyone otherwise.