If you want a watch, just get a watch that either has ant+ or bluetooth, then get an HRM that is either ant+ or bluetooth.

For the most part, the watch can do a pretty good job at detecting your heart rate without the strap. If you like the Polar watch, I'd go for it. You can get it from Amazon for $130 and have it this afternoon if you're a prime member:
https://www.amazon.com/Polar-M400-Sm.../dp/B00NPZ7WNU