Changed the oil in our main daily driver, probably was a bit earlier than strictly necessary but it was past the service mileage stipulated in the manual and it’s above freezing finally. Managed to not make a mess and didn’t run into any issues. Even torqued the drain plug to within spec. Then got it washed to get rid of the salt crust from the past few weeks and wash out any oil drips from the filter the got on top of the plastic air guard.
You don’t need a flat surface. I do mine in my sloped driveway. Just be careful with the jack (or use ramps) and be sure you’re filling with the proper amount. Can’t help much with the weather though other than suggesting you get really fast at it (I can do it in about 10 minutes easily) and use some scrap cardboard boxes to lay on.