I'm in the same boat. I'm doing a combination of fenugreek, blessed thistle, and goats rue for herbs. The goats rue was suggested to me by an LC for women with insufficient glandular tissue. They do seem to have helped a bit but I still supplement. I also make barley water and drink a lot of non-alcoholic beer.
Have you looked into donor milk? I'm getting BM to supplement from a friend with an oversupply and occasionally I can find more through human milk for human babies on Facebook.
I supplement with a lact-aid. Perhaps he might like that better than the sns? From what I understand the mechanics of it are a little different. I also stick a stuffed animal in his hand while nursing so he will tug on that rather than the tube.
Motherfood and Making More Milk are two great resources for foods and herbs to try.