Welcome!!
Take a big breath I know is a lot to take in at first but, it gets better and easier with time.
Let us know a bit more about Mimo like if he has any other issues besides diabetes, how old is he ? how much does he weight ? is his weight ok?
I do suggest you take a look at the food list Bron mentioned above, any food that is 10% or less in carbs in that list would be ok for Mimo, depending on the Fancy Feast pate he was getting maybe you do not have to change food some of those pates are less than 10% in carbs and is ok to free feed actually in most cases is even better to avoid high rises in blood glucose because of food
There is a forum for Lantus users that has a lot of very good information about that insulin that I do recomend you to read because it will help you a lot this is the link:
http://www.felinediabetes.com/FDMB/forums/lantus-basaglar-glargine-and-levemir-detemir.9/
Please do consider home testing specially with 2 units of Lantus is quite a big dose to start and it could be dangerous
And ask all you want