My house is a bit like the Forth Road Bridge - almost ongoing, but I want it to be sale-able (if necessary) without needing stacks of work.
DDs and I have door wreaths for Spring, Summer, Autumn, Halloween and Winter, plus one for Christmas that goes on for a couple of weeks. DD2 loves the USA and has one for Thanksgiving too.
I change my lounge curtains, even though I don’t close them very often - I think this might have been started because of coal fires - textiles got grubby and smoky. However, my Autumn/Winter are darker colours, making the room seem warmer.
I change cushions for nature inspired ones - robins, squirrels, hares, etc. Everything gets rotated and lives in the bottom of a spare wardrobe when not in use.
It’s a change without costing a fortune.