I'm a low supply mum too but I don't take any supplements or lactation goods. Like you I also make 30ml-40ml for both breasts. Realised that I yield more when I hand express after pumping. I will get atleast 10ml-20ml more for one side. Also try to latch as much as possible. This will your stimulate milk production. We make more milk in the morning and night. What I normally do is after baby has stopped latching for 20 mins in the morning, I will pump for 25 mins. Learnt this from Instagram by a lactation nurse. And yes, definitely surprise by the amount. I manage to build a milk stash too! Currently I'm using Haakaa and an electric pump but more to Haakaa cos easier to wash. When your baby latches, put the Haakaa on the other side and it'll collect your meltdown so it does not goes to waste. This is how I also manage to build a milk stash. I also use it as a pump when I feel that I'm gonna leak.
Latch your baby as much as possible. It helps a lot. Pump after latching.