To get the most out of the programs in the book, you want a HR monitor with GPS. One great, simple option is the Garmin Forerunner 35, which you can get online for less than $100. As with all wrist HR monitors, you want to get a compatible chest strap for accurate HR readings, NONE of the "optical" wrist sensors are accurate, especially when running. You can use any strap that is ANT+ compatible, there are a lot to choose from. Beyond this simple unit, you get more features, extended battery life, etc. as you spend more $$, but you certainly could use the 35 for a long time as you grow as a runner. Based on my personal experience, anything from Polar, Suunto, Garmin & Coros is quality and generally reliable. Hope this helps!
Thank you very much - this is super helpful and is just the info I needed. I didn't understand from reading the product descriptions that the chest straps didn't come with a watch and vice-versa. That's a big help.
Of course, happy to help. Shout if you have any more questions, it's a confusing market :)