Hi amypdx,
The first place I would start your research is post #1 here which has the basic information, steps and guidelines you will find most helpful. If you do decide to make an online purchase it’s always a good idea to start with some local testing to make sure you have a good sense of the types of materials and mattresses you prefer.
I would also look at a mattress and an adjustable bed as separate purchases so you can make good value comparisons for each of them separately and together. You may find better value for one in one place and for the other somewhere else. Adjustable beds are much easier to compare in terms of function and performance than mattresses which are much more subjective and based more on personal preferences.
You can see some of my thoughts about ordering from Costco in post #4 here.
The better options or possibilities I’m aware of in the Portland area are in post #2 here. You have some very good options available including one of the members of this site which probably the first place I would visit. They have some great quality and value mattresses available (including latex) that you can test in person. They also carry adjustable beds.
The adjustable bed thread here should also be helpful with your choice of an adjustable bed.
Phoenix