Water Bottle Carrier--I really like this with the extra pocket. I would put a hard bottom in it just for stability.
Free pattern: Ruth's hot water bottle cosy
Hot Water Bottle Cover Tutorial and Pattern
Hot Water Bottle Covers - Free Knitting Pattern
Felted Wool Hot Water Bottle Cover | The Purl Bee
Adorable hot water bottle covers by Kelley
Going to make these hot water covers for friends for Xmas
clever design for hot water bottle cover, the bound open edges in the middle to slip it in and out #blankets #craft
LilyRibbons: Hot Water Bottle Cover Tutorial--I like this design, it makes more sense for filling.
Cabled hot water bottle cover - free pattern on Let's Knit site