By now, hopefully, you not only realize that you need IPv6, but that you need to replace any ISP that is not able to give you IPv6 connectivity with one who can.
But now, you have a different problem. Your ISP probably gave you more addresses than exist on the whole IPv4 internet, just for your company network. How do you use them in a way that is sustainable, easy to understand and leaves room for future growth?
RIPE (The european IP registry, i.e. the folks who hand out IP addresses in Europe) are distributing a document written by the folks at SURFnet (the Dutch academic ISP) on how to do this.
It’s not a step-by-step how-to, instead it lays out your options and tells you what you need to consider when choosing the best set of options for your particular situation.
You will find the document at How to prepare an IPv6 address plan.
Note that if you’re still in the equipment procurement stage (in which case, what are you waiting for), you would be best served to read Requirements for IPv6 in ICT equipment which makes it easier to write your procurement requirements. That’s another RIPE document, prepared by Jan Žorž of go6.si, Merikke Käo of Doubleshot security and Sander Steffan.