Dd is similar to your ds. I invested in a couple of aluminum canteens. The ones I got fit inside her doidy. Why not just take what ever you want him to drink in a bottle and pour it into a cup when he needs a drink. It's a bit of a pain but she gets a drink. Years ago I encountered a no spill cup which I would try if I ever found one, I think it was a Tommie tippee one.
I have used both but prefer a plastic one we put our own drink in as they tend to squeeze the cartons all over the place. They started off with a take away cups with a straw in the middle from cafe nero, DH and I filled them with water to try and stop them drinking all our coffee!
What about something with a straw for out and about? My two youngest both happily drank from straws from around 7-8 months. I used to take a bottle of drink for DD and fill up her doidy cup as needed when out and about but it was a bit of a faff.
DS has never been keen on drinking anything other than milk. He's 10 1/2 months. Rejected Tommee Tippee sippy cup early on. He occasionally drinks diluted juice from a bottle but only 10ml if I'm lucky. The only success I've had is with a Doidy cup at mealtimes - he is starting to hold it and drink from it. (He'd rather drink from my glass though!) I was feeling all relieved and smug till I realised that won't really do when I'm out and about will it?? Do I need to persevere with the sippy cup? Try a soft spout one? I'm hoping to get him off the bottle around a year