Apple Watches or Garmins are pretty decent in terms of heart rate monitoring to be honest, I'd certainly get one as they provide all sorts of good informatio on top of heart rate.. As CV says, just take it easy until you finish C25K. Once you can run 5K without stopping, you can then start trying to run longer distances AND doing interval work at a faster pace. Both of these will get your fitness up no end. Once you have got up to 5K, start looking at park runs, a nationwide (and indeed, worldwide) series of 5K runs on Saturday mornings at 9am. They're great fun, there are loads of them, and the people who do them are all moslty really nice. It's a fantastic community, it really is.