@craiggrannell @mattgemmell Have you tried the turning on Vehicle Motion Cues to address your vestibular triggers on iPhone? (Settings/Accessibilty/Motion)
My wife turned this on while on a long road trip earlier this year when she needed to do work on iPhone. It helped then, but she's left it on and says it helps throughout the day even when not in a car.
I have no idea if this will be of benefit or not to your issues, but it might be worth a shot.