G'day Jase,
Wristguards as you say are helpful for correcting wrist problems and teaching correct methods. However, they are not overly helpful in correcting backswings and followthroughs.
The best advice I can give you on working with backswings and followthroughs - and keeping the delivery straight and on target - is to get two objects, such as two airmchairs or something similar, and putting them far enough apart so that your arm can just fit through (without the ball). Stand behind the chairs, and practice swinging your bowling arm through this gap. You can do this forwards (followthrough) or backwards (backswing). This teaches you to keep a straight swing, and it really does help teach you accuracy which can translate to the lanes. Last time I actually got around to doing this drill I shot 787 and the next week 298. So from my experiences it works (I've just been slack with exams, hence why I haven't done it lately).
My advice is to give this a try before anything else.
Hope this helps your game mate,
Tim Reichel.