Just do what you want. If you just want to give your kids presents and not have decorations yet go with that. Christmas dinner well that's just a meal, you can have it as simple or as fancy as you want.
We didn't have a tree until the second year we were out but the smell of a real tree fills your house for weeks and is gorgeous. Your kids will adore decorating it. If you feel odd doing it pour yourself a glass of wine and chill out that's what we did and it became our tradition. Get the box of decorations down from upstairs, pop a bottle of bubbly. 😀
Write a few cards for people at work and neighbours if you feel like it, they'll be delighted.
Your kids will have such a brilliant time and yes they are pretending they don't mind not joining in. They hate it just like you did but they're young enough to forget it all and learn all new Xmas traditions. Have a wonderful time!