Who's going to be hosting it? If you get the choice have it at your place so you know where everything is and can have a little lie down if it all gets too much. Let/expect DH to do a lot of the legwork, shopping, cooking, hosting, cleaning up. It's your Christmas too.
My Mum, Dad and SM have spent several of the last 5 or 6 Christmas days together with my siblings, partners, kid, but my parents had been divorced for about 20 years when it started so plenty of water under the bridge!
DH and his ex barely speak and my DSC would be horrified if they suddenly started wanting to spend time together, it's not that sort of set up.
I don't know OP, everyone's different and you're a good sport to even consider it. Don't make life harder for yourself by taking on too much or trying to make it all perfect. You're going above and beyond already and have nothing to prove.
Really good advice above to see if there's anyone you could invite for the day as well, might dilute any tensions and you'd have someone there you know well, so there's less opportunity for am awkward triangle of mum, dad, kid, and you killing yourself hosting around them and having a horror of a day.