Create my own high-gluten flour by mixing vital wheat gluten and bread/AP flour?
Yes, and it is very easy. I do it all the time. 

You only need a very simple calculation. You don't even have to be precise. 

If you do want precision, you will have to find out 1) how much of your flour protein is gluten, 2) how much of your "vital wheat gluten" is gluten, and 3) how much gluten content you need for your recipe. Then use a simple rule-of-three calculation to get the amount needed to add. 

I usually don't bother, because 1) and 2) is information which is very hard to find, and due to the large difference in gluten weight and complete weight, imprecision from not using true proportions is minimal. What I do is: 


Look up the protein content of your flour (usually printed on the package), for example 9.6 grams per 100 grams 
Look up the gluten content needed for your bread recipe. If it is not specified, 12.5% is usual for bread flour. 
Add the difference in vital wheat gluten. In the example above, add 2.9 g of vital wheat gluten per 100 g of flour. 


This doesn't produce exactly 12.5% gluten content, but I think that it is within the tolerance of most recipes; indeed, not all commercial flours are exactly 12.5%, they vary with brand and season. 

I add the powder to the flour and mix it well before making the bread. If I am using a preferment, I add all the gluten to the preferment and make the non-fermenting part with AP flour only, so my gluten can benefit from longer autolysis. 

I have no direct comparison with "true" bread flour, as I have never used it. But my breads requiring bread flour turn out good for my standards. There is no problem with bad distribution, the dough turns out very smooth and evenly elastic. There is a pronounced difference to using AP flour only.