After going Christmas week in 2015 (never again!) we have gone the week before Christmas the last two years and those trips have been fantastic!! We are very much like you. We are not park commando types and like to do resort activities and schedule a lot of downtime and lots of non-park things to do. The weather the last two years we have gone has been gorgeous. Not a drop and of rain, and, yes, we could have swam every day (though, I have to say, we have been lucky. The weather can be variable. Here is a record of the temps last December:
https://www.accuweather.com/en/us/o...er-weather/32835us?monyr=12/1/2017&view=table You will see the week we went, it was in the 80's!)
The parks were a bit crowded, but completely manageable. If you plan on going to MK (and not going to
MVMCP), I would suggest going to MK on a party day and getting out by 4 pm at the latest when the party guests show up. We did a lot of non-park stuff like HDDR, DS (we did The Void Star Wars experience there). We visited other resorts to see the decorations (we stayed at CCV and visited GF, CR and BWI), went to the Boardwalk one night, etc. We also did everything we wanted to do in each park.
We will be going back that same week this year. Especially if you aren't parks all day people. You can go to the parks, get in your must-do's and then go enjoy what your resort and other areas of WDW have to offer. I LOVE the week before Christmas!