What is your favorite Easy Upgrade step-by-step from ThisOldHouse.com?
My current favorite has to be the rustic headboard https://www.thisoldhouse.com/how-to/how-to-build-rustic-headboard, we still can't stop admiring the work we did! Have to say, really enjoying the ideas on here. Not an upgrade, but we also followed the pumpkin carving guide here that the kids did (with other adults of course) together with slime, which we also found online.
I would mix and match textile. For example, curtains with bedding set in complimentary colors ( i got mine here https://www.nostra.lv/ ). New pillowcases, carpet, plants are great too. An affordable way to bring new colors to the home.
Mix and matching sounds like a great idea.