I wouldn’t apply a generic floor-area percentage yet. First establish what the 190 m² includes: normal living space, storage, basement, stairs or other areas with different utility. A 2-bed layout over that area is unusual enough to make the breakdown important. After that, exact micro-location...
Getting the holding period wrong could make the apparent cheapest offer quite expensive. I would build a table showing the initial outlay, monthly instalments, outstanding balance and stated exit charge at several dates, rather than selecting one assumed refinance year.
Then test affordability...