My name is Yuchen, one of the instructors for off-season spin. If you’re not planning on buying a new watch/computer anytime soon for this sport, I would highly recommend the Wahoo Tickr. It’s what I use, and it works with pretty much anything because it’s dual broadcasting (ie. both ANT+ and BLE). This means that you can use it with your phone, or with a Garmin should you decide to get one.
Whenever I do indoor training, I generally use the Tickr with my iPhone because of the large display and I can see everything. But then, when I do a brick workout, I’ll power up my watch, and it’ll pick up my heart rate with the same strap.
Hope this helps!