There's no reason for a vampire not to make coffins on their own. They have plenty of time to pick up new skills and it's more feasible to have someone in the community to make it without the involvement of food.
Also it's difficult to build up a loyal customer base for a product that lasts for decades or centuries when you yourself will only be active for a couple decades.
I'm not exactly tech savvy but I looked I to it recently and it seems like the lower end Garmin Forerunner series is what you're looking for. I might get a Forerunner 45 for 120€ myself but you can probably get earlier models like the F35 for cheaper.
It seems like Garmin is the only brand that offers decent quality sensors at a lower price range.
Low body fat will plummet your testosterone levels which then leads to a low sex drive and erectile dysfunction... Oh we we're thinking about different EDs XD
Also your ED makes more sense in context of a girlfriend but we're in the fediverse after all.
I recently watched some videos about the effects of low body fat on your body and I didn't read your comment properly.
Thanks for pointing it out. I'm aware of that but I'm at 17% body fat and my goal is around 10-12% so my testosterone levels should stay at a normal level.