So far in standard, slow foxtrot has been my hardest dance. I can do the steps, but I struggle with the whole twisting the upper body and making my upper body less stiff and more fluid... more foxtrot-y. I feel if I try to make it more fluid in my upper body, I lose my frame. Any tips? What can I do to not be so stiff? Does anybody else have this problem?
It sounds like you are holding your frame by bracing it (i.e. contracting every single muscle at almost maximum strength, for the duration of the dance). As a very simple illustration of how tiring this is, try squeezing a ball (tennis ball, golf ball, stress ball, any sort of ball really) as hard as you can (or as hard as you hold your frame) for the length of a dance track. Now compare to how much less tiring just holding the same ball gently for the same duration is - you don't drop the ball, you don't move the ball, but the ball still stays exactly where it is with much less effort.
In ballroom, many people learn by getting static positions (usually the starting "setup" position) poked, prodded and manipulated into the correct position. A lot of people never get the lesson about how to maintain this position
through movement, where the joints in the body *change* their relationships to each other, that *different* muscle groups must be activated *differently* through *different* movements to maintain the *same* position. Because they don't get this idea, a lot of people end up "one size fits all", which means they apply so much force to maintaining their frames that no matter the stresses placed on the frame, it stays the same, but this excessive force ends up looking very braced (because it is!), and it is also extremely fatiguing. Been there, done that.
Economy of effort (i.e. "effortlessness") (also known as "tone") comes from applying the *minimum* amount of muscular energy required to achieve a particular body position and/or movement - any more and you get "tension" rather than "tone", any less and you get distortion of body position. Note that the amount of energy and combination of muscles required to maintain "tone" changes through each different movement. Different body positions and different movements each demand different levels of exertion from different muscle groups, one size does NOT fit all - obvious when stated, not so common sense, in my experience.