What about MT. Vernon WA? It is still a reasonable drive to Seattle and the same to Vancouver BC. Bellingham and Everett are both close by too.
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Skagit County in general may serve as a happy medium in terms of what you are looking for. It is interesting that the average high is in the 70's during the summer, can be in the 40's during the winter.
Parts of Snohomish County may work too. Marysville is a place that comes to mind.