Oh dang! You really did get hooked. These arent known as the highest quality sensors but, these “Arduino sensor kits” on Amazon or wherever you shop, theyre a good bargain and gives you sensors to work with and learn with. These gas sensors are fun to use too and you can get halfway devent readings from as well.
Depending on how deep down the rabbit hole you get sucked into this, Id suggest also learning the other half of this hobby, the electronics side… I have this book among many Simon Monk book, he has a good way of explaining things so they make sense and dont overwhelm you. This is a good beginner level book and the topics are broad while not getting too far into the weeds with electrical theory and fun calculus eqations. I can send you some photos of inside my book if youd like to see some of it.