I used my leftover sock yarn to knit a quick cover for my hot water bottle. Held double it is equivalent to DK weight yarn, so you can use that instead. Technically this is a large tube sock knit toe-up. I have demonstrated the whole process in my reels on Instagram if you would like more visual props.

Skill level: advanced beginner to intermediate; need to know Judy’s Magic Cast On, increases, ribbing, and stretchy bind-off.
Finished dimensions: about 7.75 in / 20 cm wide, and 14 in / 35.5 cm long measured when empty, not on a water bottle.
Suggested Yarn: sock weight yarn, total of about 3 oz / 90 g or 400 yd / 365 m
Needles: size 5 (3.75 mm) circular needle, or size needed to obtain gauge.
Gauge: 10 st and 16 rows = 2 in (5 cm) in stockinette in the round