Hi batmannorm and welcome to the Mattress Underground 
Thanks s for your insight and sharing your experiences with the Plank mattress! Seeing how others feel about a mattress can be helpful to a certain degree…but, as mattresses are such a subjective item, someone with your same affect, Stars (height, BMI, sleeping position(s) and any underlying health conditions) and PPP (Posture & alignment, Pressure relief and Personal preferences) can find a mattress you find firm not firm enough.
In person testing can tell a consumer a good bit, but the true proof is sleeping on it for a period - it can take 4-6 weeks to ‘break in’ a new mattress and for one’s body to acclimate to it as well, which is why it’s always wise to major sure there’s a good return/exchange policy, wherever one shops!
While the Trusted Members of the site have all been vetted for quality, transparency in materials and components, and generous return/exchange policies, some sleepers don’t feel comfortable online shopping for a mattress. For them, I recommend our Mattress Shopping Tutorial for tips on how to identify a good local retailer or mattress manufacturer.
Again, thanks for sharing your own mattress journey here - and we wish you many more years of comfortable sleep in the future!
~ Basilio