Hi, I didn't read all of the responses so sorry if I'm repeating, but first of all, it sounds like you've done an absolutely marvelous job to date, so congrats on that. It's amazing you can even keep a 7 month old going on almost nothing but milk if you think you have a low supply. I was in a similar situation and the minute I reduced how often I nursed, my supply just plummeted, so I would not agree that he is using you as a pacifier, I think he's just eating that often because if you have low supply, that's probably what he needs.
That said, I also agree with the comments that you might want to consider upping the solids. By the time he's a year, that needs to be his primary food source. You could think about offering solids 3X per day, do it right after he nurses if you'd like, but feed him as much as he wants (till he refuses to open his mouth/pushes the spoon away/spits it out).
For reference, my baby, who will be 7 months in 1 week, eats solids 4X per day (he just seems to like them more than milk) and a typical meal might be two ounces of milk or formula with cereal, half a jar of fruit, and half a jar of veggies.
I try to make sure there is something filling with every solid meal (cereal with milk or forumla rather than water, yogurt, a "dinner" baby food that has a meat blend, a rich veggie like avocado -- yes, I know it's supposedly a little early for meat and yogurt, but my pediatrician okayed it, though you could stick to cereal with milk/formula and fruits and veggies till he's 8 months). Just fruit or veggies by themselves won't really fill him up much at all (look at the calorie count on the jar if you want to know how filling something is).
BTW, my boy is 45% for weight and has stabilized there, but when he was on just milk, he was 25% and cried a lot more because I think we was always a little hungry. I started to supplement with formula when he dropped to 15%, so if you're stable, I don't think you need to worry too much, but it does sound like you can up your solids.
Good luck!