This is just the dilemma I faced when I got another dog recently - a mastiff called Kaddie. She's a week younger than Wicket, but already weighs in at 25kilos

I've never let Twinkle onto our bed, so that isn't a problem, but I was a bit worried about how to deal with the sofa situation
Twinkle has only ever been allowed on the sofa when invited up (usually in the evening), and now Wicket too, the reason being that if the children are up there the dogs like to try and steal their toys/food

We bought a
huge squishy bed for the living room, which is a 'communal' area for all three dogs to lay during the day, and Kaddie is more than happy laying there in the evenings while Twinkle and Wicket have some 'sofa' time.
I did feel a bit mean the first few times, but kaddie hasn't tried to get on the sofa, so she obviously doesn't mind, and there haven't been any dominance issues because Twinkle and Wicket are alllowed 'higher up'. Also, it would be impractical to allow them all up on the sofa......me and DH would end up sitting on the floor!

They know they are all loved equally! xxx xxx