I seem to recall you tried a ride on lawn tractor but not enough traction.
At my house in France I had a nasty scare pulling a load of logs for the wood burner up to the house when the Westwood lost grip and jack knifed back down the hill. It just had the normal turf tyres on so I got a set of agri/chevron tyres fitted and had no more problems skidding. That might be a cheaper option.
Actually I got another Westwood so I have one for grass cutting and the other with the agri tyres for moving the caravan around the garden and general moving jobs.