I'm working through this book called "Scrawny to Brawny" by JB and Mike Mejia and in phase 2 they really stress bench presses, squats and deadlifts. This is all understandable but my problem with the bench press is that I have no one spotting me since I go to the gym solo. Is it OK to do the bench press with dumbells instead or is that unacceptable? Thanks a lot!!