I wear a 38 in the Gizeh which is my FAVORITE shoe ever.  I tried these in a 37 and 39.  The 37 might have worked if I didn't have a bum big toe that cannot touch the shoe for ANY time or I am in pain for days.  I am waiting on the size 38 M to arrive.  I want these shoes so bad.  Purple is my favorite color and this is a purple that will go with almost anything.  They are cute in my opinion and look great with jeans.  I accidentally tried the soft foot bed (different color) which is much smaller due to the extra padding.  I can't do the soft due to foot issues.  To be certain if they are soft or original check at Birkenstock site as only certain colors are certain footbeds.  These are original.  ****UPDATE**
I received the 38 M yesterday and they are perfect for me.  I would guess if you have longer toes you would have to go up a size as some reviews have said.  But...... I tried the 3 sizes and the same size I wear in the sandals is my size for the Boston.  FINALLY !!!!