I ended up buying the Garmin Vivosmart 4 that
@keepswimming talked about. I really like having this watch. It shows me patterns in my PEM (2-3 days), things that cause me to really crash (eggs), and things that are helpful in bringing my hr down.
I like the body battery setting the most. On the watch it shows where I'm at currently with an arrow that shows me if I'm going in the right direction (up), staying the same (maintaining) or doing too much (battery draining) so even though it does not have an alarm to remind me of going outside my hr parameters, I still use that as a reminder to rest when I need to. (It also does show heart rate and I use that too but I generally look at the body battery reading more.)
I do wonder if this watch might not be helpful in another way. Perhaps it could lend a visual to healthy doubting family members on how we're doing especially if they had one of their own to compare it with. IDK ???