It’s going to be a cold end of Feb/Mar so I’d go with stocked lakes over trying some of the harder stillwater. And the ones along the way to Portland stocked with steelhead are a blast: Fort Borst (no boats allowed, can walk around it and backcast fairly easily) and Kress Lake are both stocked with steelhead Jan-Mar.
Aside from those your stillwater will be more of a struggle for fly fishing until we get warmer weather.
You could swing the Cowlitz and get ready to call someone XYZ expletives, EFL gets hit kind of hard along with SFT but they have good access, Kalama (nymph water with a couple swing spots down low by the park). Couple others I’ll let you discover, focus on the less big name winter run waters for less crowds.
Various skinny water west of i5 going out towards Cathlamet that are fun. Just depends what fly rod weights you have/want to use, if you want to swing, nymph, how far you want to walk/drive etc.