I struggle to get up in the early mornings, but it's part of having small children (and unfortunately one of the parts that sometimes sticks when you have SEN children). Has he not got over this in seven years? That's appalling.
Your DS likely has ADHD. That means it's highly likely either you or your partner does, too. Do you think it might be him? ADHD can make it difficult for adults to get up in the morning (sadly, not children, though you may find DS turns into a grizzly bear when he's a teen as well - fun on school mornings). That's the root of my own struggle BTW.
Unless there is a genuine trade off here - say he goes to work stupidly early during the week so that he can finish early to spend time with the family, and/or he goes to bed really late because a child gets up for 3 hours in the middle of the night and needs supervision, and/or he's extremely apologetic and accommodating of you having unlimited naps later in the day - you need to be taking turns at weekends to get a lie in. And that means the person whose turn it is to get up gets up with minimal disruption to the other one and then manages it as best they can.
I tend to do a bit of sitting up in bed and letting DS2 mooch around the bedroom until he gets destructive or wants to be loud and then I get up into a really warm dressing gown and fluffy socks (sensory - leaving the warmth of the duvet feels unbearable) and immediately go to brush my teeth and then make coffee.
I don't change DC out of pyjamas immediately (just a nappy if needed) and we make extremely simple food for breakfast - I favour toast or microwave porridge, DH prefers to cut up apple and put in a snack bowl with dry cereal or crackers. TV is allowed in the morning and I don't tend to do much actual parenting other than damage limitation. We stay in the most childproof room.
Most important - there is never any sniping about how "I got up at 6" or "I only got 3 hours' sleep" - competitive tiredness helps nobody. We have a kind of "open nap policy" - if it doesn't interfere with plans then we let each other nap without question. I guess we probably get out and do less than most families seem to at weekends, but we see weekends as for relaxing and recovering from the stress of the week, not packing as many activities into as possible.