WOW, hadn't been to your website before I made my suggestions to you. You have a beautiful website!
My only suggestion would be that instead of listing your collections alphabetically and then manufacturer. It might be more helpful to list the manufacturers and then their collections. Then one could see if you had any of the collection they were short in and see the new collections available by the manufacturer. Since many of us have favorite manufacturers it would help us if we couldn't remember the name of the collection as they would all be displayed together. Many websites do this and I look at what manufacturers I like and then go on to some of the others I'm not so familar with...I love to see the pictures and colorways available from each designer.
Ghostrider has great ideas also. I guess you could drive yourself crazy trying to fix it the way everyone thinks it should/could be. I have been buying online for years and it's truly up to me to understand how to learn the different ways of getting to what I want on their site. If it's too difficult I do go elsewhere but I don't think you really have any problems with people understanding how your website functions. I've been on here way to long today and am losing my ability to think and write properly.
Bottom line you do have a fabulous website!