Can someone PLEASE help me? Trying to "fix" double charge on shipping!

[xoxoloveme80]

Hello everyone!

At present, I offer two items in my store. I am trying to get it set up so that the following happens:

1-2 of item X  "OR" up to 6 of item Y = small flat rate price

3+ of item X "OR" 7+ of item Y "OR" ANY combination of X & Y = medium flat rate price

This pertains to orders domestically (I'm in the US) OR internationally.

Is there any way that this can be done? Can anyone walk me through this, please?

Thank you