I think the people questioning what's hard about having a baby in lockdown are being seriously thoughtless. I had my first baby in non-lockdown times and she was by far my harder baby, but it was so much better being able to do baby groups, visit friends, go to coffee shops etc. If we were having a bad day we could just find somewhere to go, and it made it all pass so much quicker. I had my second baby in June when restrictions were lifted a bit, and it has still been tough.
I would definitely look at what @SinkGirl has posted about Possums - they have a website to. It will really fit in with your approach of not trying so hard to make the baby sleep, and just getting on with your day. I did something similar with my second baby and while we still have rough days, I enjoy my life so much more for not making it my life's work to (unsuccessfully) make him sleep. I shudder now thinking about how much time I spent trying to get my daughter to sleep - and honestly, despite me not doing this with my son he sleeps better at night and is generally more chilled out than my DD was.
The Possums approach goes against everything you read on Mumsnet about overtiredness, sleep windows and overstimulation. It works on the idea that babies do actually get bored and under stimulated, and if you meet your babies sensory needs they will sleep easier and they will be less grumpy.
It's really hard with a tiny baby in lockdown to keep them occupied. My DS is now 8 months, but things that worked for us early on were:
-Pottering in the garden, either sitting with on my lap on the bench or wandering around with him in my arms looking at plants, trees birds etc. For a change I sometimes sat on a bench in the park and watched the dog walkers go by.
-Lying him on my legs and singing along to Disney hits from my youth. If he was being squirmy and restless he quite often settled to music.
-Sharing a bath with him.
-Supporting him in the window looking out
-Just moving from room to room really frequently.
-Sensory stuff like bubbles, tickling with feathers, space blankets (very cheap and effective for newborns), fairy lights.
-When my husband was home he'd play the guitar to him which he always loved.
Sorry for the epic essay. I really feel for you - I don't know how I would have coped with my earlier baby in lockdown. And your post really resonated because I think the Mumsnet obsession with "all your baby problems will be better if you can only make them sleep every X minutes" is actually sometimes quite harmful for the mental health of new mothers.