I found this a few months ago on Canyon's site and this fits great on my medium e150 - It cost me £30 and you get 2 bottles that are 400ml each so plenty of water and room!
A lezyne side load cage caught my eye when I was mooching around my local bike shop. Gave it a go for a tenner but will definitely need to find a smaller bottle!
I’d recommend the Fidlock 450 too, true it’s not cheap but you get what you pay for in my opinion, it’s rock steady and looks great too, not the biggest bottle but if you buy a water filter you’ve as much water as you need as long as there’s a water source on your route, but where abouts isn’t one in this country ?