How much space you need will entirely depend on what you need the space for.
DH and I share 800sqft, we just sort of downsized from 1500 sqft. I say sort of, because our old place had one room used as a gym, a bunch of storage we didn't need, a second bathroom that was rarely used, a giant laundry room, where we stored bikes, and a home office we no longer need as DH's job needs have changed.
Our new place is a large 1 bedroom in a building with a gym, bike room, and laundry room outside of the unit. We're also minimalists with no hobbies that we do inside the house, and we spend a decent amount of time apart for work, so don't need much space from each other when we're here together.
Our new place feels bigger because each main space is bigger and better laid out than the old house, which felt huge but cramped at the same time sometimes.
Layout is a huge factor, but again depends on what you need the space for.
If you are a crafter/hobbyist who needs a hobby space as well as a home office, has a child who plays drums, and you're really into Kayaking, then you will need A LOT more space than I do, and you will want a lot of that space very separate.