What type of fields would you need to add? Will those fields change the price? Have their own inventory?
Let me know!
Depending on what you're looking to accomplish, there is a good chance Product Extra Fields will suit your needs. Their support email can be reached here. They offer a 14-day free trial and then charge $3.99/month.
Let me know if this helps and it does what you are looking for. If there is anything else I can help you with, please let me know.