I don't know details of your situation but it seams to me we have a cart before horses case here.
To use an example, you might be also asking:
What should be the minimum force to open a car door (because people are lazy) so they would buy the car
I perfectly agree with you that forms longer than absolute minimum can have a negative impact on conversion rate but perfect forms will not 'BOOST' your sales. It will not happen because as in the 'car example' it is not what really makes people buy things.
People will do a lot to buy a product if they want this product. So to boost your sale you should concentrate on making people want to buy it. It is similar to making them want to sign up to a service. So let them try it and like it and if the price is OK they will buy it (and an imperfect form will not stop them). See diagram below.