I understand you OP. Me and DH are figuring this out too (for slightly different reasons - he was brought up with very little and wants to make sure LO never experiences that, I was brought up with money thrown at things and want LOs Christmases to be as fun as mine were, all with the added complication of us waiting a long time to become parents via adoption).
You have at least 1 teen so Christmas is likely to be a bit expensive but could you give a family trip or experiences as gifts instead of ‘stuff’?
We tend to have a rough budget but aim for 1
big thing and a few small to go with it from Santa (our LO is young so play kitchen with some wooden food, pots, pans and apron) then a mix of stuff they want and need from us (so he would have had PJs, socks, tooth brush anyway but we got those plus some toys, books, puzzles etc).
A year or so ago there was a little SM trend of people asking kids what they had for Christmas the year before. A lot of them could name maybe 2 things - but when they were asked what they liked about last Christmas, they could all give some example of something small that involved others (going to see Santa, the lights, putting up the tree).
I’ve done the same with LO and he remembers having Mickey Mouse socks, having lots of lights and watching The Grinch in bed with me while eating popcorn.
Its quite eye opening - maybe try it and get an idea for what matters to the dc and focus efforts on that.
Lastly, if you over spend but can afford it, dont worry too much. But when its all wrapped, if it looks like too much, you can always take some out of the pile and put them aside for birthdays or return them (spoken from experience)