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Hello, We are an e-commerce & content site undergoing a website migration and redesign in the coming months.  We will be getting an entirely new website.  Many of our URLs will be changing: Current URL setup: www.mysite.com/catalog/SKU12345/product-title-here
Future URL setup: www.mysite.com/catalog/product-title-here So we're aware we will be using plenty of 301 redirects to achieve this. Further to this though, we currently have a product page for each configuration of a product - for example, a single-sided bookmark has its own page and URL, and the double-sided version of the same bookmark has its own page and URL.  In our site redesign, we are hoping to consolidate each of these instances into one product page where users can select single or double-sided and the price will update accordingly.  The bookmark URLs would then go from:
_www.mysite.com/catalog/SKU12345/bookmark-single-sided  _(call this URL A for simplicity)www.mysite.com/catalog/SKU67890/bookmark-double-sided  (call this URL B) To (after migrating to the new URL structure for the new site, and the now-consolidated single- & double-sided product pages):
www.mysite.com/catalog/bookmark  (call this URL C) What is the best way to make this transition without losing too much of our SEO value?  I understand there is nearly always traffic loss with URL changes but I'd like to at least minimize the damage as best I can.  We have backlinks and ranks for many product pages so I want to make sure we pass as much of this as we can. (And is this at all further complicated by the fact that URL A & B won't exist on the new site, and URL C doesn't exist on the current site?  Does this impact the use of the 301 redirects and if so, how?) Are we better off to approach this page consolidation after the site migration and treat it as a separate project?  This is something that is important to our user experience, and is definitely a change we want to make. Any advice is appreciated - thank you! I'm a fairly beginner-intermediate SEO so this is all somewhat new but I want to be able to at least convey some understanding to our developer of what we need to do.  I was able to find this discussion (https://moz.com/community/q/merging-pages-and-seo) which describes a similar situation and solutions if we were just consolidating the pages but doesn't quite have the complicating factor of the entire site migration happening at the same time. Thanks so much!