Here is a 12 seat Washington. I tried basing it off of the 2012 map, including parts I don't really like about it. I kept the majority-minority district (WA-09 is 51.4% non-white). I kept the way they crossed the Cascades, with Klickitat latched onto the third and the 8th stretching from East King/Pierce to Eastern Washington.
WA-01: 60.0% Obama, 53.3% Murray
WA-02: 55.4% Obama, 50.4% Murray
WA-03: 52.4% Obama, 54.1% Rossi
WA-04: 58.4% McCain, 63.6% Rossi
WA-05: 49.8% McCain, 56.9% Rossi
WA-06: 58.0% Obama, 53.4% Murray
WA-07: 83.4% Obama, 80.4% Murray
WA-08: 54.0% McCain, 62.4% Rossi
WA-09: 66.9% Obama, 62.4% Murray
WA-10: 55.6% Obama, 51.5% Murray
WA-11: 54.4% Obama, 51.1% Rossi
WA-12: 63.0% Obama, 55.1% Murray
D - 1, 6, 7, 9, 10, 12
R - 3, 4, 5, 8
S - 2, 11
I kept the partisan breakdown about the same... WA currently breaks down to 5-4, which would translate to about 7-5 with twelve seats. The Democrats would have six safe seats, the Republicans four, with the 2nd and 11th districts as swing. I might try to alter Snohomish County later to make the 2nd a little more Rossi.
I did get rid of the current silly split of NW Washington. With smaller sizes, we can achieve the same goals without it.
The 3rd did technically vote for Obama, but I think the Republicans would definitely be favored there.