Hi there. I run an 18+ social/casual raiding horde guild on the joint realms of Lightbringer/Mazrigos, and it sounds like we may be what you’re looking for.
Although we’re an 18+ guild, quite honestly the average age is a lot higher - the majority of members have busy real lives with work, relatives, children, etc - we basically play WoW to relax and take our minds off real life for a while. Or, if the mood takes us, hit something hard in the face until it drops loots (in game!).
We have a wide range of interests from members in-game … from those who raid fairly regularly to those who never raid, and everything in-between. A lot (but not all) are altaholics … there’s virtually always someone levelling a lower level character.
We tend to raid twice a week - Wednesday and Friday from 9.30pm to midnight server time. We have no rules about having to raid x times a month, nor do we “trial” raiders or anything like that. We put raids up on the calendar in-game - if you have the gear level for it, and can join for the full duration … you just sign up. Sometimes we can accommodate people if they can’t join for the full duration (for example they can’t attend for the first 30 mins, or the last hour, etc) - this is of course role dependant and depending who else is signed. We’re aware that people sometimes have to go afk - crying baby, child throwing up, child’s head stuck in a toilet seat (yes … that last one HAS happened to a child of mine 
). Come to think of it … All of those have happened to me lol.
As far as the guild itself is concerned … it is based on the ethos that we’re recruiting people, not characters. We’re looking for PEOPLE who will fit with the rest of us … don’t expect too much (we’re not hardcore raiders, we don’t raid mythic, we die, regularly, and we probably spend far too much time having a laugh during a raid night) … and are willing to sit back and enjoy the guild ride.
We chat mainly via text - in-game guild chat, discord channel with lots of various text chat channels, etc - mainly because that’s just how we’ve always done it, but also because a lot of us aren’t able to be pinned to the computer, with headphones on, talking to people, because we’ve got stuff going on, or potentially going on, irl, all the time.
We do use Teamspeak for voice comms during raids, and occasionally use discord chat for stuff like dungeons, M+, achievement raids, etc. But it’s the exception rather than the rule.
I know you mentioned you’re looking for a “quality over quantity” guild … I think we kinda fit into that … in that we don’t take any new members without going through an application process to try to ensure we are the type of guild they’re looking for, and they are the type of person we think would fit. Having said that … as mentioned before, we do have a lot of altaholics … so some of that quality comes with quite a lot of quantity 
If it sounds of interest you can check out our realm advert for a little more info:
along with our website : www.darkwolves.eu
As I mentioned before, we do only take new people via application - which is on that site. If you have any questions beforehand, feel free to join our discord where we welcome guests as well as guild members, and you can get a feel for us there, and ask any questions:
https://discord.gg/gQ2uBGe