Is baby always a poor nurser on the breasts, even if you try breast compressions, or even with a lactation aid? Are you saying baby also falls asleep when bottle fed and takes little from the bottle? How much weight did baby lose and how much exactly is baby pooping? The weight gain as you describe it is certainly a red flag baby is perhaps not getting enough. Is it difficult to get baby to take the breast, or will he take it fine but just not nurse vigorously? I would suggest nursing baby more if you can, and maybe feeding baby more often overall. If using the sns is not working, you can supplement with a bottle and allow baby to "finish at the breast."
I would not suggest measuring that baby is getting enough by baby behavior. While falling asleep at the breast or when eating is generally normal, a baby who is not getting enough may also seem very sleepy, fall asleep quickly at the breast or bottle and not cue enough. How many times a day is baby cueing & nursing or feeding? It should be very, very frequent, no matter how baby is fed, a minimum of 10-12 times a 24 hour day at this age. You also may want to pump 10 times a day or, if that is more than you can handle, as much as you can if baby is nursing that poorly. When exclusively breastfeeding, the most accurate way to measure if baby is getting enough is weight gain and output-poops specifically-at least 3-4 poops the size of a US quarter or larger per day. I do not know how formula would change this as far as output goes, you can talk to your LC about that. Please make sure weight checks are always being done accurately and carefully, on the same scale, with baby naked or in a dry diaper only.Do babies ignore food if they are still hungry or fall asleep at the breast constantly if they need more food? I try to give him more formula but he always falls asleep during feedings or stops eating. I hope this means he is getting enough food.
As far as your milk supply/production 'going down,' that cannot ever be measured accurately by pump output-and there is a possibility things will improve in that department once you are using the right kind of pump. However, it is still very inaccurate to measure production capability by pump output no matter what pump you use. Be very careful about losing heart over pump output!
Have you looked into getting the books that have been suggested? IN particular, Making More Milk? Meanwhile, try www.Kellymom.com and search low supply, she has lots of articles on how to build supply. There are lots of options for supplements. Frankly unless you enjoy the tea, I think you would need the higher dosages of supplements in a pill form. But you should be able to discuss this with your LC.
I believe the availability of screened donor breastmilk varies on where you live. If you are in the US, you can inquire about buying breastmilk from screened donors from a Human Milk Banking Association Milk Bank. https://www.hmbana.org/ There are online resources that facilitate private milk sharing and selling, these sites are kind of like social networking, they do no screening, so a mother has to do her own screening of donors if she chooses.
For more on LLL’s policy on informal milk sharing: http://www.llli.org/release/milksharing.html
If you are you asking if breastmilk being a third of your babies diet would make a difference in your babies health, studies would suggest definitely yes. While the more breastmilk the better of course, The benefits of breastmilk are there no matter how much baby gets. ie, some is cerrtainly beter than none, from a health standpoint. But you as teh mom have otehr considerations and may find the effort simply to great. That is OK, you will know when you need to move on should that time come. But it is very early days and you have been trying to do this without support and with two major contributign factors: namely, your baby is not nursing vigorously and well and you have been without the right kind of pump. Even a mom with no biological/medical barrier to good milk supply would likely be struggling with milk production in that case.Would it even make a difference if it were only comprising a third of his diet?