A "basic digital" is probably the best choice. Alternatively, one of those classic tall analog lever action scales where you have to slide counterweights on a lever. You still see them in gyms and some doctor's offices. However, those are likely to be much more expensive.
The spring-based dial ones need to be calibrated every time, as well as of course the springs seem to get deformed so it's a question of being accurate.
What do I mean by basic digital? I mean it has an old style LCD digit display, and the only option is to show pounds or kilograms, settable with a switch. It's also powered by a single AA or CR2032 (coin shaped) battery. The original CR2032 battery that came with mine lasted a good 13 years, not even kidding. It's not fancy in that it has no Wi-Fi access, no Bluetooth, no special app needed to work, etc. You probably do NOT want one of those.
The WiFi, Bluetooth, etc. uses much more power, meaning batteries need to be replaced more often. This gets expensive fast. If it relies on an app, you hope it'll still be supported in 5 years and would still function on the latest Android. Getting 20+ years of use might be a thing of the past. You don't want to have to replace it every few years now, do you? Of course not. Also, the really basic digital scales will use simple chips, that won't be affected by this chip shortage going on right now.
Basic digital models can be found at Target, Wal-Mart, etc. for around.. $20-35 maybe? Also, out of curiosity I looked around last year. You'd be hard put to find a model that doesn't go up to at least 400 lbs. Most seem to show in 0.5 lb and 0.2 kg increments.
3 years