Means you got some tiny sit bones!

That's about 105 mm. Mine are about 180 mm.

Basically the centers of the "cheeks" of the seat should be the same width as the centers of the sit bones, or else you'll end up weightbearing on soft tissue and tendons or be concentrating weight too hard on the bones (if you are perched on the very edge of the seat or over the metal frame of a leather seat). At the very minimum, the seat needs to be as wide as your outside-edges measurement. My seat is 210mm wide. Most comfortable seat I've ever sat on.

With a 105 mm width, you've got a lot of choices of seats.