Double ditto on Toms comment.
A vari drive which is all belts save the F_R & diff is what i would be looking at.
If the towing load gets too much the belt just slips
If you are fine with old mowers, any one of the older models fitted with an Eatons tranny.
Down side is they are getting long in the tooth.
If the wallet will allow then go for a sub-compact tractor with either belly mount or up front mowing deck.
Down side is these are real machines built properly to last for decades ( like mowers used to be ) so are priced accordingly.
However when you consider it will most likely out last you, money well spent.