There are TWO things we have had done that I smile about ALL the time.
1) Side return. It is amazing. It transforms the house. Get one now and you'll never look back I PROMISE you. But. And its a big but. We lived through it and it was hell. Truly truly awful. We did it and I am glad we did but I don't think I could do it again. Imagine someone walking around your house every day with a big bag of dust and tipping it upside down on everything.
It is worse than that.
Before we had ours done someone said to me "its like it has snowed in your house. But its dust." My reaction was "yeah right" but its true. Only whatever the opposite of exaggerate was they did that. Its like it has snowed heavily.
2) Basement. WAIT! Not the big dig out basement that costs millions but getting the basement tanked and some proper lights and some wood on the walls painted white. We then had tiles put down. Cost about £5k and it has turned the basement into a proper room, albeit a room for short people. We then had proper stairs put in and it has all the sports kit, two fridges, washing machine, tumble dryer, wine etc. Its amazing. Just to be clear we didn't dig out at all but just make it light airy and dry.
Get those two things done and your life will be enriched immeasurably