Arthur flies a Cub. Having flown a Decathlon I would say it is aerobatic enough and certainly has more space and better access than a Cub. The only fly in the ointment may be that it is a certified design and so would carry a deal more paperwork to modify the controls to suit.
I would guess ease of access is always going to be a challenge with the majority of aerobatic designs, most of which have 'top entry' arrangements. The Beagle Pup is possibly an option and although ageing, there are a number of aerobatic Austers - possibly worth thinking about.