Hi MagnoliaSleeper,
This would certainly add some uncertainty to a mattress purchase it’s not really possible to quantify or predict how much of an effect the pregnancy may have on testing for her longer term needs and preferences or the effect of all the changes that will happen after the baby is born.
If I was in your shoes then the options you have available after a purchase (and after the baby is born) to fine tune, exchange, or even return the mattress based on her actual experience would be an important part of my personal value equation. If you are looking at an online purchase anyway I also agree with jankdc that a component mattress from one of the members here would make sense and could be a very good choice because you can re-arrange or exchange layers after a purchase to customize and change the mattress if it’s necessary and you can also have a split construction where each side of the mattress is customized for each of you. The tutorial post includes a list of the members here that sell mattresses online and many of these sell component latex mattresses with a wide range of designs, features, options, budget ranges and return or exchange policies that would be well worth considering and in most cases or for most people may be better “value” than a Costco purchase (you can see my thoughts about a Costco purchase in post #4 here).
Just to clarify … while Bedrooms and more is certainly one of the better options in the Seattle area, have some high quality mattresses (including 45th Street Bedding), and are on the Seattle list … they are not a member of the site (you can see the membership list here).
Phoenix