ratio of flour to liquid in bread
This works out to a ratio of 77% hydration (see this answer for an explanation of the term), which is a very good choice for this flour mixture and should not be dry at all. So the problem is most likely in your measurement. The best you can do is to use a scale, because volume is very unreliable. In  If you absolutely insist on measuring by volume, you will have to invest time in getting to do it properly - not packing, levelling well, etc. 

Also, you should not be mixing the flour into the dough, you should bne kneading it. If by mixing you mean you are stirring it with a spoon, this is only an early step, you will have to continue kneading the soft dough in the bed of flour until the flour has been absorbed, and then continue for enough time to get a nice elastic dough (about 15 min of hand kneading). I am sorry if this sounds patronizing and you are already kneading properly, you did not describe it in detail so I am trying to exclude the possible culprits here.