Save your calculations - you can go back later and judge how well you modelled your future selves.

My wife and I did something very similar 7 years ago when deciding between 3 flats, and recently came across our backs-of-multiple-envelopes calculations. We only considered the one we actually chose and estimated our current weightings for the different spaces. In our initial judgments we had vastly overrated our future use/value of the outdoor space, substantially underrated the kitchen and lounge rooms, and entirely ignored hall and loft storage space which has turned out to be decidedly non-negligible.

We are very happy in the flat so this is not an exercise in regret, hindsight or possible alternative universes - but made us notice that if we are flat hunting again, outdoor space is likely to cost more than it's worth to us.