I used Polycam. I’m not sure if it’s 100% accurate down to the inch - probably not but it was quite close. They have a floor plan editor now but I haven’t tried it.

As for planning the new space, I sketched it out - I might have used their tools, might have also just sketched it out on paper.

Once I had my plan, I marked it out using masking tape just to sanity check and everything fit as expected.