I am trying to work out the attributes for a new venture.
Basically I want to offer the following

A5 leaflets 1 sided 150gsm Gloss
Qty's 1,000 / 2,500 / 5,000 / 10,000

Which I have done using attributes 2,500 + £35 / 5,000 + £70

I want to add a percentage for changing the material to 170gsm Silk and also a percentage if printed BOTH sides.

I have set option names and option values but they only add a fixed amount.

for example 1,000 2 sided adds £20 but 2,500 also adds £20 (I want it to add £30)

From reading through help files etc is this even possible?