Everywhere I've been this week, I've seen people with broken wrists from falls. Undoubtedly due to lots of wet leaves and such, but there are things you can do to help yourself - both prevention of falls and mitigation of the effects of falling:

First off, do plenty of tai chi walking - this will not only help you improve your awareness of where your weight is, but will also help you walk around with slightly bent knees as your default in everyday life. Straight locked knees are just asking for trouble with falling.

The next thing is to ask your instructor to show you a balancing exercise, where you drop the knees, the butt, the centre of gravity,  while simultaneously bringing the elbows in to the tantien and the hands up. You really need to practise this exercise until it becomes reflexive. It will counteract the automatic tendency to put your hands out to save yourself, which is how people are getting their wrists broken, while also lowering your body, so that even if you don't save yourself, you are falling from much lower down and therefore going to incur less damage, hopefully landing on your butt, which will give you some bruising, but a bruised butt is far less awful than broken bones.

Get an instructor to show you this exercise - as with  all things, they look easy, but they need that outside input to get your practise correct, without flailing around hoping for the best...