I wanted to avoid Garmins new paywall model. The avoidance of sending money to the US is a bonus. Changed 645 for Suunto Race S. Tip - you can download the Suunto app and use it for an activity or two to see what it does - obv you don’t get much data. There is ecosystem shock when you change from Connect (not connect plus because fuck Garmin) but you get over it. Maps are amazing.
I am skinny - if I am not actively swimming in fresh water I am sinking (sea is different but sea comes with waves which is an added complication). If I am tired or nervous then I have to fight with my subconscious to be calm and stay safe. So I would add mental strength to the list for a first time swimmer. And even then I’d say don’t go out of your depth.