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?
morning weetabix (a half) with milk and then a milk feed (6am)
milk feed (10am)
lunch and a small milk feed (1pm)
milk feed (5pm)
supper after bath and milk feed (730pm)
there were times she would not need the milk at lunchtime (she never has it now, just water in a cup) and she now has her tea at 5pm with a drink of water again, so just with progression she has stopped the feeds of milk at these times
also, she sometimes doesnt have the mid morning one, i wait and see if she is looking for it
At six months your DS is still really young, and I think your HV is a bit over-eager. At this stage weaning is more about getting them used to the idea of eating. I would keep up the milk feeds and introduce solids - if it helps I BF my DD (8mths) first thing in the morning, then she has breakfast, a nap, then BF after her nap, lunch at around 12-ish, then nap, BF, then tea and then BF before bed. With DS I followed GF and cut out the 11am feed when I introduced protein at lunch, but haven't done this with DD - no idea why!