You can get Float and Tigermylk in the following shops, and re-use your glass bottles. You pay a £1 deposit on the first one, and whenever you bring an empty back (with the lid!), you can swap it at the counter for your new bottle of and get your £1 deposit back.
You can also get a tasty Float coffee at a few selected cafes (orange pins on the map)
*Map correct as of 9th March 2022