Have a changing mat and all the essentials (crate with nappies, bags, wipes, nappy cream, eczema cream if baby needs it, antibac wipes for mat, antibac gel) one upstairs and one downstairs.
Have a similar crate for everything you might need. Painkillers, lansinoh, nipple shields, snacks, water. So everything is within reach.
I hated muslins, didn't find them absorbent at all. I used the white flannels from Ikea, Krama washcloths. My daughter eventually chose a flannel as her comfort object. Not a teddy or a soft toy, a bloody flannel. She still has them now, at nearly 3. A gross soggy flannel that she sucks the corner of. So maybe I shouldn't recommend them!
Amazon prime.
Dry shampoo, for when you haven't showered in 2 days!
For things which you only have one of, but use day and night, get a canvas bag so when you first go downstairs in the morning you can carry it all with you and not have to keep going up and down stairs when you need something. Breast pump, infacol, thermometer etc. Then when you go upstairs for the night take it all with you.