Touchpoints. So door handles, light switches, taps. A basic sink with expensive taps will look better than the reverse.
Natural materials. Cotton curtains looks better than fake silk. Wooden or metal window frames are higher end than PVC. Agree about flooring, it probably counts as a touchpoint if you walk around in bare feet as much as I do. Plastic flooring (that includes LVT) is never as high end as environmentally friendly flooring like wood, linoleum (real lino, not vinyl), cork, or wool. Tiles are hard wearing if need that.
Agree the basics being cohesive feels like money has been spent and that doesn't have to be expensive, white walls and white roller blinds will achieve that along with your expensive touch points and natural flooring. Then you can introduce colour with the changeable things like furniture and soft furnishings.
Can you incorporate a utility room upstairs? So much more practical.
I never understand why people say this, how is it more practical to have to carry wet washing downstairs to hang outside?
A well planned layout with plenty of electrical sockets in the right places and considered lighting where you actually need it, not just a grid of spotlights or a central light. Coloured cord is having a moment rather than default white plastic.
I think you can save on your furniture, use a mix of carefully chosen IKEA, second hand, high street, hand made and high end/design classics in each room. Again avoid plastic, better an old bashed about but solid wood chest of drawers than a new MDF version. You don't want all new in a room, it creates a bland room. In fact all old furniture that is well chosen will look a milliontimes better, although you probably want to reupholster a lot of chairs and sofas.