Yes yes yes to decluttering and streamlining your wardrobe. Less stuff and less choices is the best way to live more simply.
Minimise time online and take the time to sit and do fuck all with no distractions. It's amazing how calm you can feel in just a few minutes.
Go for walks. I discovered the joy of walking in lockdown. It's such a simple joy. I'm in peri and I swear my evening walks keep me sane.
Just say NO. If you want a quiet evening or weekend, prioritise it and don't get swayed by people trying to make plans.
Meal plan and batch cook (that's the answer to everything isn't it!) but it keeps life simple. I'm never happier than when I have a bolognese sauce defrosting on the side 😆
Make a plan for housework. Yes it's fucking boring but I feel calmer if I know I just need to do floors today, beds tomorrow, bathroom on Saturday or whatever. Basically get one job done per day then it doesn't build up.