First of all, congradulations!
I have looked it up for you, there is really no 月子中心 in Seattle and you are right, they are mostly in Southern California. I would strongly suggest you to 坐月子, considering your age and if you plan to have another baby in the furture, 坐月子 is very important!!!
Since you have no one to help, I would suggest you to 坐月子 in California where most 月子中心 now offers 待產中心 and in-house service, etc. Check out this site:
http://tw.search.yahoo.com/search?p=%E7%BE%8E%E5%9C%8B%E5%9D%90%E6%9C%88%E5%AD%90&y=%E6%90%9C%E5%B0%8B&fr=&fr2=sb-top&rd=r1
I`m five months pregnant now, althought my mom-in-law will help me 坐月子 but I`m still doing some research for give myself more options. You might not notice the great difference now if you did not 坐月子 but just look around these middle-age American on the street, you may notice why they age so quickly compare to Asain ladies.