How old is your ds?
You are right to do this gradually, and sort of let your son lead the way. If he doesn't seem too bothered about his bottles, then yes you could start to drop some.
I find this whole thing with HV's telling people to drop a feed a bit iffy, because each child is different and needs/wants different things. Mummy's know best in my opinion! So trust your instincts and you'll have a happy son!
The only time you need to think about stopping a bottle, is maybe if he suddenly stops wanting solids (and you're sure this isn't down to illness or teething). That will be a sign that he is filling up on bottles.
I breastfed dd on demand - so had no idea how much milk she was getting, so i feel if i were to bottlefeed my next child, i'd still be more inclined to listen to the child than look at the quantity of milk/food they were getting. Does that make sense?
HTH