These days I feel like this kinda people are everywhere. Like I'm talking with 2 of my friends and they are constantly gossiping and bad mouthing some other people. When one of them leaves, other starts to bad-mouth him as well. So when I'm not around they might do the same thing about me. This really makes me uncomfortable. Sometimes I get influenced by them. I'm a bit shy and introverted person. So when I try to start a conversation I choose one of those gossip topics since that is guaranteed to make a conversation. Later I hate myself for bad-mouthing others.
People might say to leave them but they are good people at heart. And if I do I don't know if I'll find good friends again with this personality of mine. I don't actually know what I should do

There's no harm in small talk (in your words, gossip). Thats how you meet people. And even if you're good friends with someone, that doesnt mean that you'll always be discussing deep topics with them.

Now as you said, if you worry about whether your friends are talking about you behind your back, the long and short of it is that you cant do anything about it anyway. So dont let that bother you. Also, if you want, when the badmouthing starts, you can try to discreetly steer the conversation away from it (So you dont have to feel like you did something wrong)