You will save yourself a lot of time and trouble by just buying some Caputo 00 pizzeria flour rather than buying a weaker 00 flour (lower W rating) and trying to get the protein level up by adding another flour.
According to fellow member pizzanapoletana, the specs for the Caputo 00 pizzeria flour (in the blue bag) are as follows (from another thread):
Wet Gluten 32-34
Falling number 340-360
From the above, you will note that the Caputo 00 pizzeria flour has a W number of 240-260 which is just right for making pizza dough. (The W number represents the results of a test that is used to determine the strength of a flour by determining the rupture point of an inflated bubble of dough.) According to fellow member Ron Molinaro, the Caputo 00 pizzeria flour is a blend of European grains and North-American Manitoba. This makes for a "stronger" and better flour for pizza making, with better absorption (hydration) and elasticity. The blending of the two flours essentially emulates the practice in Italy of blending 85% Italian grains and 15% Manitoba, a practice which, according to pizzanapoletana, "started after the Second World War, when they would add some Manitoba flour W400 (max 15%) to their Italian flour (W180)".
So, as you can see, the Caputo 00 pizzeria flour is a blend that is fine just as it is, and there is no need to try to replicate it by using a weaker flour and trying to increase its strength. Maybe it can be done somehow, but I don't know how you would know which flours to blend and in what ratios to get close to the Caputo 00. I have seen the Manitoba promoted by Italian millers in Italy, but I have not seen any places that sell it at the retail level in the U.S. I did on one occasion not too long ago combine 85% Bel Aria 00 flour (which is weaker than the Caputo 00) and 15% King Arthur bread flour and got good results (reported at the Caputo pizza/biga thread), but I would only go that route today if I didn't have access to the Caputo 00 flour, which is becoming increasingly available from several sources.