I work from home, but its quite a brain engaging role if that makes sense?
And i make sure i go for a fast walk twice a day, do about 8500 steps.
Always eat dinner around 5, 5.30, always eat relatively healthy also
so LISS cardio is good and the fresh air is going to be good for you. So definitely keep that up.
To baby step into it, I'd consider adding some form of HIIT cardio. Swimming, 5-a-side, Tennis, squash, hill sprints (if you're brave). Just something that will be more intense, harder on the body making you more tired.
Also not against the supplements. Multi vits, Magnesium, Melatonin (would rec this), are going to help. Have a search online for supplements to manage your Cortisol too. Cortisol is the stress hormone and there are natural herbal supps you can take to mitigate these spikes.
Outside of adding some weights/resistance training into your routine, the only other thing I could suggest, which I've never done, which is very new age, would be some form of meditation practice. If you have an intense cognitive role, I imagine you'll have a lot going around your mind quite regularly. You need some release where you can forget these things. Thinking about it weights may be my version of this. On walks I'm always thinking, but with weights its about doing the reps, increasing the weight, it forces your focus onto something and clears everything else out (lest you drop a heavy weight on your face!).
Maybe trial some of the above for a month. It's all health conscious, positive changes. Worst case even if you don't sleep better you just feel better about yourself.
If that doesn't work I'd suggest you then look at diet, have you added something new recently, have some ingredients changed, when are you consuming caffeine, have you tried removing things etc etc. But I'd do the above before worrying too much about diet because it seems unlikely you've had too much change dramatically in a short space of time.