SW Dover White (their most popular off white) or SW Alabaster would go well with your wall choices. Both of them are warm whites and are light and airy. My first choice with the Blonde and Sassy Green would be Dover White - it's got a very delicate touch of yellow/gold in it. But Alabaster has a lot of fans as well. Get Color To Go Samples, paint some foam or poster board and tape it up on the ceiling to see what you like best.

I would begin with a new area rug that has colors and patterns to wake up this very colorless space. Find something you really love, with colors that make you happy, and make it larger than what you have so that it has impact. It should be a thin rug that looks right over the carpet you have. Find colorful pillows that work well with the rug. Since you have a wooden coffee table, find end table made of metal and glass and position them next to the couch, with lamps that are large enough to give adequate light to this space. Look for large pieces of art that make you feel something, not just something that will "look good". Have books and plants in the room to furnish it and give it personality. Your home should reflect who you are and what you love, and not just follow rules of what looks "right". If you love what you have and it reflects your taste and personality it will look very much better than just "right".

Out of pure curiosity can I ask why you picked two different whites for your walls if they are both north facing? With the two choices you have made I would probably go with Chantilly lace as the white for trim throughout the home. Ceilings could either be Chantilly lace in both rooms or match the walls in both rooms. Alabaster and Ceiling white have an LRV of 82, Chantilly Lace is whiter with an LRV of 92.2. No need to cut any of the colors. If you do cut Alabaster with such a little difference between the two colors it may just look like a mistake instead of an intentional color choice.

The ceiling work sounds like a mess... yuck... if the walls don't absolutely need painting, money could be spent on wall work of dusting them, and cleaning them...