So, my books on Buteyko breathing have arrived and combined with a ton of internet research on it, I feel that I'm ready to start this experiment. I was taking my control pause wrongly, the idea is to stop holding your breath the instant that any involuntary movement occurs in breathing-related muscles such as the stomach or throat. If you stop holding your breath at this point you won't gasp for air and can continue breathing at the same frequency and volume as before.
Using this method my CP is around 22 seconds, though this drops to around 13 seconds at some points in the breathing exercises (apparently due to buildup of CO2 and tiring of the nervous system). My resting heart rate before the exercises was 100bpm and afterwards was 112bpm. It's actually supposed to decrease so I've done this incorrectly. However, this was my first ever attempt at the exercises so I should improve in my method and also my body should adapt along the way. Apart from these exercises I'll also be breathing through my nose more religiously (have been doing so in the past 3 weeks but occasionally if I get out of breath I'll use my mouth again), and trying to cause small amounts of air hunger throughout the day. I will also be taking up physical training again, as you can see from my heart rates, I'm not the fittest guy in the world (no training in the past 10 months).