From my experience raid leading, forming a group with people who've done boss 'x' not always guarantee success.
Well organized guild groups succeed because they know their individual roles, know how everyone else plays and work well as a team. Pug groups fail not because people are ignorant of fight mechanics, but because they're fatigued, complacent, or suck at working with an unfamiliar team.
I had the same problem as you not too long ago - solution is to join a guild. Our guild often takes on people with very little raid experience, and they're often the best to take on because they're more loyal to the guild, have more fun, and persevere in progression. Just need to find the right group of people mate.
The alternative is to start your own raids, which is daunting at first but also a lot of fun if you enjoy responsibility.