Does he have a specific reason? Or just trying out his “muscles” on Dad? Maybe if you simply say “You’re going, now get up”, leave the room expecting him to do so, he will go that particular Sunday. After Mass, take him to a restaurant or drive-in food place and get a cup of coffee for you and a shake or hot chocolate for him. Nothing major, just a short break for the “guys” to have time together.
See what happens the following Sunday after that! If you have a pleasant, non-confrontational time with him after Mass, without discussing the homily, etc…, just Father/Son time together, he may decide it’s worthwhile to get up on Sundays!
Is he staying up too late on Saturday nights? Out on a date or watching tv until well after midnight? Setting a time when all the kids (according to age) are expected to cease tv, video games, or whatever, and go to bed might correct the problem right there. I had a time I had to be home, and ready for bed until I was 18!! That was the rule and one of the few that was inflexible. Also doing expected daily and weekly chores was not optional. Same with getting up for school (although I loved school as a kid, so no problems there). I did, however have a time when I had to be home (usually 10pm on Fri. and Sat., by 8pm if allowed to go out at all during school days) and a time for bed (generally 10:30 or 11:00 on weekends, MUCH earlier on school days.) This carried over to summers as well. Earlier during the week, later on Friday night, but Saturday night was earlier than Friday, because I had to get up for Mass on Sunday – and I went to Mass alone, as I was the only Catholic and usually walked to my Parish, or took a bus if a longer distance, and did so by myself from age 11 onward.