if you are going to go with milk as a priority, I agree with a lot of these suggestions, especially warming it, and also with the you can get calcium, D, etc. from other foods if milk is just not gonna work out ...
... also try different brands (I do organic, and Organic Valley, because it is pasture-fed, the milk from different 'bottlers' tastes different ... so my kids happily drink the Organic Valley milk from New Seasons' supplier, but the Organic Valley milk from Fred Meyer's supplier (I presume a different facility, as the cartons were even a little different for a long time) not so much ... I know when I was a kid we could drink the Alberstons milk and the Safeway milk, but there was somewhere else that sometimes we would get and it was just NASTY ...)
...rather than adding chocolate, add a smidge of vanilla ... TOTALLY works. Warm "vanilla milk" is still a big sell around here when I can't get the kids to calm down and chill out for dinner or bedtime, and vanilla adds no sugar ;)
On the other hand, I am a big believer in the kids needs to be part of the weaning decision ... but I know not every mom can let that happen, and I weaned my first "early" for her at 22 months (my others weaned at 16-ish, 20-ish, and 14-ish) ... but I still see the effects of weaning my first before she was ready to let go of that mommy-time.
Pray/consider/walk in love. Watch your baby for what he needs to make this milk thing alright :).
I was recently telling someone, I can't imagine who was the first human to think, hey, I bet _I_ could drink milk from that hoofed animal ;). There are large chunks of humanity that literally don't carry the genes to deal with that ancient choice by a few ... four genetic groups in Africa and one in Northern Europe provide all the adult-lactose-tolerance in the world, they think now ... so, play it by ear ;).