Back in 2015, I bought these scales:
They automatically record my weight (using wi-fi) with Google Fit. Over time, it has allowed me to build a long-term and detailed record of just how overweight I am.
That exact model is no longer made or supported by the company, but they work just fine for me still. I think that the key feature here (compared to some other “smart” scales) is that these connect to wi-fi – so you don’t need to worry about connecting them to your phone on blue-tooth or similar.
These days, it seems that Withings has three models:
Withings Body – Just records your weight, which is all I ever wanted.
Withings Body+ – Records your weight, but also your “body mass”. I couldn’t get the body mass recording to ever work on mine, so I’m skeptical of this.
Withings/Nokia Body Cardio – All of the above, plus also heart rate.