As it is starting to become busy season again, I am looking for advice!

Does anyone have any suggestions on seats for baby to use while riding in the enclosed cab tractor/combine/hay mower/etc.?

Right now he is 5 months old and can sit up (but a little unsteady). The carseat doesn't fit in the cab and the "buddy seat" doesn't have a high enough back that I could strap him to it.

I'm looking for something that will work from now until he's 2 or so, and preferably with either enough recline and support to handle the bumps or a 5 point harness.

I don't mind spending a little money since we will probably have more farm babies and I am also open to sort of "making" something out of other products ( I have considered the possibility of rigging up a stroller or high chair seat.)

ANY suggestions welcome!!

(P.S.- For anyone concerned, Yes, I am aware of the safety risks of having a child in the tractor or using a child device not as intended, but sometimes there is not another option besides having him in the tractor with one of us)