How to find twinks who are big?

So basically the title says it all I am a bicurious never done it but watched porn about it and twinks who are big down there always turned me on so much. I always said I’m straight but now I don’t think so I get hard even if I think about it.

My girlfriend gave me a green light to try with guys and it just made me more excited.

What should I write to my Grindr profile or how common is it in gay community to go to a one nighter or go with guys like me to just fuck?

Also how should I tell my girlfriend that later I want to try out a MMF?

I don’t mean to insult anyone I just don’t know much about this community and I want to try it so much.