Hey Kelvias - I believe we have exactly what you’re looking for. We are a fairly casual raiding guild with our goal to only do AOTC each tier. We run Mythic + frequently and hang out in Discord a bunch 
We are also looking for more friends for 8.1 and beyond. The guild has been together since 2007 so I don’t believe we’re going to fall apart a week after you join either 
Here’s our recruitment post if you’d like to learn more. Best of luck to you in your search for a new home. ~Moonpie