Health tracking devices with selfhostable backend

Are there any good ones? I currently have an Apple Watch and sync it to OpenWearables, but I'd much rather not have my health data in any cloud. Is there any hardware for that? I don't care about the type of hardware. It can be a ring, watch, band, etc. Needs to be compatible with iOS. Health metrics I care about: HRV VO2 max HF Sleep + phases Not must-haves, but nice to have: Skin temperature Breathing frequency