There are numerous chillies from around the world with different flavours. I tend to use the long thin green chillies, which in the Asian grocers are simply called green chillies. They are larger than the Thai green chillies, which are super-hot, but a lot thinner and indeed hotter than the more bulbous chillies such as jalapeño. If I buy a lot, I freeze them and then use them from frozen when required. For these recipes, buy whichever chillies you like to use and you are comfortable eating. The trick is to taste all the beautiful flavours of the dishes without overpowering them with chilli. When starting out, err on the side of caution and use perhaps half a chilli with the seeds removed and then next time try leaving the seeds in. Adjust amounts to your own individual requirements.