So, I never used a hot water bottle. My Mom bought me a heating pad about 10 years ago that I loved. This is the new version of it, I believe. It's expensive but worth it. The moist heat penetrates deeper. Having said that, my pelvic floor physical therapy said it's best to alternate cold and heat, as heat can worsen the inflammation of endo.

The other good thing about this heating pad is that the switch has to be held down for it to be on. So while it's still "not advised" to use it for sleep, I did all the time. I was just very careful to place the switch where it wouldn't be accidentally turned on while I slept.

https://fsastore.com/Battle-Creek-Thermophore-M...

Here's my list of other tricks that help my pain:
I alternate Ibuprofen (Advil) and acetaminophen (aka paracetamol or Tylenol). I like TENS units, but IMHO, don't spend more than $30-40 because many are overpriced and it's bologna that they charge that. Warm Epsom salt baths help too. I also have pelvic floor physical therapy exercises and there’s lots of yoga for endo videos on YouTube. Here's links to two of my favorites.

https://youtu.be/KQdN000kpqM
https://youtu.be/OfO6BZb6A7Q

I also have compounded suppositories of Flexeril (muscle relaxant) and Lidocaine (numbing agent). There’s several different formulas of them, so ask your doc if you want to look into that. When I have to be away from my heating pad, those Thermacare menstrual heating pads (or generic) are helpful. Some users swear by peppermint oil to the belly but it was too strong for me. I never thought to cut it with coconut oil though. This oil blend to the belly helps me.

https://www.mylola.com/products/essential-oil-b...

The second my pain starts, my hot water bottle comes out. It’s the only thing that helps me. I have 3 at home, 1 in the car, 2 at my parents and 1 in my classroom at work.

The best thing that’s helped for me is a heating pad and a long hot bath. Also, drinking LOADS of water.
I really hope you feel better. Take your time and rest a lot.

I have never used a water bottle, but have you tried a hot shower or bath?

You're most welcome.