I think you can afford to lose some of those oz as I would imagine there is some dairy solids being eaten too, cheese, yoghurt, white/milky sauces, these all count towards the daily dairy intake. i would just switch one bottle for now and work on the second one after the first is weaned/switched.
I always advise to drop the BT bottle first because keeping larger fluid intake in the morning rather than evening helps to increase bladder size and helps towards night dryness when the time comes (not yet but eventually) and it is important now to brush teeth before BT after any supper or milk. But it is totally your choice. If you drop the BT bottle and switch to a cup and solids snack/supper before bath/BT it doesn't matter if the milk intake drops, the morning milk intake could also increase if you do this (keep as bottle just for now whilst the BT bottle is weaned). I can guide you through this if you feel the bottle is an important part of your BT wind down routine and he might be disturbed without it?
For the larger milk drink that you want to keep (for me then that's the morning one) how about go back to the bottle but snip the teats and sit him upright on your knee for them, this increases the flow and makes it faster and more like a 'drink' rather than sucking on a teat. Then after a week or two continue with the bottle but remove the teat and pop in a wide straw. i used the disposable kind (with the bendy part) as I tried some of the straw cups and never felt the milk fully cleaned from inside the straw. The disposable straws I washed out and put in his craft box for various activities, colour matching, counting, making play doh aliens with long bendy arms etc etc, so they weren't wasted.
If it is in the bottle he can see it is milk inside, recognise the bottle and will see the straw as the new part, it's less of a change all in one go. I tried this several times over a couple of weeks with refusal and when he refused I just popped the lid back on and let him have the teat (big hole being snipped) then tried again a couple of days later. Another thing with the straw is you can trap some milk in the end making a vacuum with your finger, lift the opposite end to his mouth and release it so he gets the taste of milk. I demonstrated to mine then offered to him. When I ditched the last bottle completely I didn't use a cup with straw but a new bottle so the association was not with water or sippy cups, I got a cheap, colourful straw bottle but removed the straw and used the disposable straws. I continued to have him sit on my knee for it for a long time, so he had the comfort and also so the milk didn't spill!
You can also switch to full fat cows milk at this point if there are no known allergies.
