Product options & Royal mail shipping

[Guest basquen]

Hi,

Is there a way of entering different weights for product options? The shop sells art prints most of which are available in small, medium or large. It doesn't make sense to have each print listed as a seperate product so I've put the small product in as the main item and the other two sizes are shown as options.

For example

Main product is print 1 (small - 30cm wide) = £45

Also available (from drop down product options)

medium - 40cm wide= +£20 (ie £65 total)

large - 70cm wide= +£60 (ie £105 total)

The problem is that shipping costs are different for each option.

small = £5

medium = £7

large = £10

Any ideas how I should go about this?

I'm hoping to sort out shipping by weight but have been holidng back until I can get my head around the new Royal Mail pricing that is coming into force in the UK in August.

Thanks

Nick