I recently moved from paddling a 24" wide boat to paddling a 19.5" wide boat and still use the same paddle. Unless you need quick short paddle strokes, I don't think there's any need to go to a shorter paddle.

If you think you need to go to a shorter paddle, there must be a shop in your local area where you can rent a paddle for the day. Hopefully they will allow you to apply the rental fee to the purchase cost if you decide to purchase a new paddle from the shop where you rented from.