Personally I love my apple watch for sleep. None of the watches can actually 100% track different stages, u would need to be hooked up and get an overnight eeg for that but, but its great for sleep/wake times and trends over time. Also it'll track your rhr + hrv automatically and keep the data so you can see trends and stuff which I find great in combo with sleep for measuring my recovery/stress/etc.
Also if u said ur feeling your high rhr maybe your blood pressure is just really high

have u been checking that every day? also maybe check your hematocrit..
70-75 rhr isn't terrible but if youre active ideally it would be lower. and 20mcg T3 is a pretty big dose which even if ur labs say that your FT3 is in range, it might be supraphysiological like an hourish after you take it and you could get tachycardia from that. I also supplement T3 but i do 10mcg when i wake up and 10mcg like mid day to try to even out the curve and prevent an energy crash later in the day.