[EdZ]

A very good drill for you would be to hit shots with a ball under the outside edge of your right foot (or a 2/4 or similar) and focus on maintaining the flex in your right knee.

You will get a good sense for how flexible you are or aren't very quickly and this will likely be a help to maintaining your spine angle and head position. Drill this with a heavy club/two clubs held together and with your eyes closed and hold your finish to check your balance. This will help show if your setup posture/clubfitting is out of alignment quite quickly because you won't be able to hold your finish in balance.