Have food and drinks in that you both enjoy and allow you to have a relaxed day.
Don't rush in the morning - get up when you want.
Have things for a lovely breakfast together.
Plan on getting outdoors for part of the day - a good walk somewhere or bike ride if you both cycle etc. There may be Christmas Day runs or swims local to you to join in with.
Decide when you are opening your presents - we always do that in the afternoon. It breaks up the day a bit more.
I also always have a good book that I'd like to read over the break on hand, and some board games that we like.
Have a lovely meal planned for dinner that is a treat for you. Something that will take some effort to make, but not require all day slaving over the stove.
Have a look at the tv guide for good movies or specials you would enjoy, or plan to watch something streamed together.
Make calls to extended family.
And just take a slow, gentle day.