I have done solo cruises to Alaska on the Pearl and the Jewel many times. I always book an inside cabin. Works fine for me.
The question would be is it easier for you to do a roundtrip cruise or a one way cruise. The Encore and the Bliss leave and return to Seattle. Some Sun cruises will also be roundtrip. The Bliss leaves and returns on a Saturday. The Encore on Sundays. The Sun's cruises will vary in length. Both the Jewel and the Spirit will sail out of Vancouver, British Columbia. The Spirit will sail to Valdez, Alaska (a new port of NCL) and the Jewel to Seward, Alaska.
Whatever cruise you do, you will have a wonderful time.