Hi Help needed,
Welcome … and I’m glad you found us 
I’m not sure what you’ve read since you found the site but just in case you haven’t read it yet … the first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort”, firmness, and PPP that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you.
When you reach step 3 in the tutorial and you are ready to test mattresses then subject to confirming that any retailer or manufacturer on the list that you wish to visit is completely transparent (see this article) and to making sure that any mattress you are considering meets the quality/value guidelines I linked earlier in this reply … the better options or possibilities I’m aware of in and around the Seattle area are listed in post #2 here.
I’m looking forward to finding out what you end up deciding … and of course to any comments or questions you may have along the way.
Phoenix