Ds was closer to 1 so a little different to you (same age gap tho as dd was prem!). But we were still feeding to sleep so I think this is what got us through the supply drop (for me I stopped feeling letdown after 1st tri). Since he was then just over 12 mths I just started introducing cows milk. I knew he wasn't getting the full milk from me (his sloppy colostrum nappies were evidence .. consider yourself warned lol). But yeah, because our feeding was more than just about the milk, it continued throughout. Grab yourself a copy of adventures in tandem nursing. It's really good.

As for the supply, I didn't do anything as it was hormonal, not a supply demand thing.