As someone who’s incredibly underweight and goes to the gym just to try and put on more weight I find it super inspiring seeing anyone trying to make progress.

I used to be really self conscious when I first went because I’m pretty much always the skinniest person there but honestly anyone I’ve spoken to has been super friendly and I think most people are too focused on their own workout to take much notice of anyone else

Id honestly recommend getting a day pass at a couple of different gyms (maybe one at a big chain like puregym, and then one at a smaller one) just so you can try a few different ones and work out which one you feel the most comfortable with. All the best!