A word of advice - there's a replacement seat widely sold for the small Yanmars, and in my opinion it crowds you too close to the steering wheel on the smallest Yanmars. I didn't know the difference until I got a second YM186D that had the original seat pan (no padding, I added a cushion) and it feels spacious by comparison to that replacement seat.
So my advice is for that tiny tractor, step up to a better, larger seat than the common 'universal' replacement.