A fine point in answer to your question OP is...you can make your 'fit' more relaxed...but you can't take a racing frame and turn it into a relaxed comfort fit bike. There is a difference...head tube angle...length of head tube...chain stay length and wheelbase etc.
You mention your can afford a Defy. I strongly suggest you buy a new bike...one designed for comfort or distance riding.
I prefer the Roubaix which has a taller head tube than the Defy but it really depends on your preference and body proportions.
I will tell you that fit and type of bike is transformative in terms of comfort and pain avoidance.
Good luck.