Sell goods in boxes/cases with different case sizes

[KindratP]

Hi all. Sorry, maybe it was discussed many times before, but I can't find a simple ready-made solution. 

My situation is followin: We sell wine bottles. For instance the product itself it's a wine "Lafite Rothschild 2010". Then same wine could have different bottle sizes, e.g. 75cl, 150cl, 300cl, etc. 

Then we can sell wines in loose bottles, or in cases. Cases could be different sizes: Case of 3 btls, Case of 6, 12, 24... 

Originally I set up bottle size and case size as attributes. But the issue is that is someone buys 4 cases of 12, it's not so obvious how many bottles purchased. Especially when several bottle sizes/wines in the basket. So it would be great to have some Unit of measure settings, where I could create an entity e.g. "Case of 6" and specify how many usual bottles are in.

Any suggestions or links to the exact modules ?

Thanks guys!