Thanks for the feedback. Glad blink step worked out for you.
As for the suggestion - I'm aware that there are a few other games that employ a scheme similar to what you're describing (e.g. Technolust), but through my own research and testing, it's not an ideal scheme for most users, because you lose a great deal of the flexibility of movement... moreover, most people don't expect motion to be stuck in one direction, but follow their bodily direction of movement.
The main thing I'd suggest if you know you can get nauseous easily from non-forward movement is to keep your hand by your side, aligned with your torso. This should be easy as it's essentially the default resting position for your arms when moving. Also there's an option for 'Simple Touch', which rejects the thumb direction and only uses the controller direction.
This way, you're only moving in the direction of your body - but retain the flexibility to turn and move without having to stop and start.
For more advanced users, simply moving in a manner that roughly indicates their intended direction of travel is sufficient to help further reduce motion sickness (e.g. if I'm moving sideways, I mimic a motion for strafing, or if I'm moving backwards, I mimic a motion of backpedadling).
As for the elevation issue - it's a difficult one to deal with outside of teleportation/blink stepping. I think a reasonable compromise is to make elevation changes optional by allowing players the ability to teleport between the different levels, or to reduce the amount of elevation changes in general.
I assume you had the comfort mode on high?