sticking to few champs

How do people stick to a limited champion pool? I enjoy playing competitive, and therefore know I need to keep a small champion pool. I have been playing since season 2 and my peak rank has been platinum. I know a big reason why is I am never able to stick with something for long enough. Over the past 13 or so years in this game I have moved trough every role. I think the problem is I do this to much. Last season I started playing TF and LB mid, then after awhile I got bored and started playing adc, then top.

Any tips on how to just stick to a role and champion and not get bored. I am currently playing a lot of Mundo top and that is currently very fun, but I know the urge to quit is coming.