Heart rate training

[sheepysheep]

Just looking for some HR monitor advice really.
I'm getting back into running after a couple of years break (busy job then baby gave me far too many excuses not to run!). Previously I was very into heart rate training - I love the science of it and find it works well for me. I used a garmin forerunner which I've dug out and it still charges and works. However, I have remembered how disappointinrg it is to use - the data it records is fab but it's clunky to use and the touch bezel is a PITA. I'm now considering getting something that tethers directly to my phone. So... has anyone had any success with just using an app plus Bluetooth chest strap? Or even a wrist band thing - they sound great as I could wear it all the time. If so, any recommendations? My chest strap is ANT+ so not compatible with my phone. I have an iPhone 6s.
I'm not worried about GPS - what I do need though is a min and max alarm that I can set myself (low RHR and high MHR so the formulae are completely out for me).
Any thoughts gratefully received :-)