Here are some tips to avoid heating pad burns:
Yes, hot water bottles do work just by using hot water ... you can get them with covers to help minimise burning to the skin. I find mine keep warm enough for quite a while ... up to an hour or more. Ample time to help soothe me off to sleep at night.
There are many microwavable products, in many shapes and sizes, rice, herbal or wheat filled, which are much safer than hot water bottles (no possibility of bursting!) ... I have quite a collection although I do find they don't stay warm for as long as a hot water bottle does, and tend to be craving more heat after about half an hour.