Both of the ramps mentioned are good ones. If you are coming from the south, Gleason (the second of the two, on the southern side of the Columbia River) lets you avoid crossing over the bridge to Washington. Depending on your timing, that bridge is a bottleneck these days.
As for a marina, any chance you are a member of a yacht club? If so, there should be several places in the area that offer reciprocal moorage. I'm a past member of Rose City Yacht Club and current member of Portland Yacht Club. Both are great facilities, with PYC offering a bit more in terms of amenities (restaurant, bar, staffed clubhouse, etc). There are a host of month-to-month moorages in the general area that no doubt offer short term options, too.
Feel free to PM me if you have more questions.
Gini