Hi Sara_joel,
Welcome … and everyone is a “noob” at one time or another 
The first place I would start is post #1 here and the information it links to which is the most important post on the forum. It will give you all the information and steps you need to make a great choice.
As you will read … knowing what to avoid (such as major brands and chain stores or any retailer who can’t tell you the real information about what is in their mattresses) and knowing who and what to focus on is more than half the battle. In most cases who you buy from can be just as important as what you buy.
You are fortunate to be near Portland because you have some very good choices there and one of them is a member of this site which means I believe they are among the best quality, value, and service in the country. You will find the list of better options in and around the Portland, OR area in post #2 here.
Post #2 here has some further options in other areas of Oregon.
Brooklyn Bedding does allow returns if the mattress is purchased from their own site (they are just starting to release their new line of mattresses there) but there are fairly significant shipping charges involved. The ability to exchange a layer a much less costly way to make changes to a mattress if your first choice isn’t quite right.
I’m not sure where you saw a “recommendation” for Healthy foundations but it certainly wasn’t from me
Post #486 here has more of my thoughts about them.
Phoenix