I've had a fitbit wifi bathroom scale for a while. Getting the data out got suddenly more difficult when Google bought them, and I didn't love giving that data to google. It's finally died, and I'm looking at replacement options.
In a perfect world, I could just go to a store and buy a "HomeAssistant Ready" scale. If I can't have that, I'd like a scale that is on my local network and exposes the last x weigh-ins as an API on the device, then I could write something to poll it.
I haven't seen anything like those, but have turned up:
a project to decode the bluetooth transmissions of a number of scales (after you build an ESP32 device for it)
I'd guess automatic history tracking. Step on it every morning and it'll automatically save your weight to Home Assistant or whatever so you can see if you're gaining/losing over time.
I don't keep track of my weight so I could be wrong here, but more/less than last time wouldn't be very helpful as your weight can vary by the day. You need a trend over weeks to really see what's going on. I definitely wouldn't use pen/paper as it's just too much data to organize and graph, but excel would be a reasonable alternative.