Simon,
Awesome to hear that you’ve found biking and have some mates to show you the way. That’s more than half the battle. Knee pads are be a great bit of kit to help build confidence and keep you progressing. In addition I’ve found that learning to roll with a crash and falling correctly is another skill that adds to injury prevention and keeps you riding.
It’s kind of hard to practice and the only way I can think to do so would be some forward rolls but kind of off to the side. Sorry if this seems odd and unsolicited but i’ve seen many new riders fall stiffly to the ground and hurt themselves even with pads where rolling out of it may have helped.
Happy riding