Welcome to the forum!
There are no 'transition' pieces to connect '0' track to '027' for a number of reasons.
First as you state, there is a height difference between the 2 types of track. That would mandate raising the '027' track to match the '0' gauge track height.
More importantly, the rails themselves are a different size; '0' gauge track being taller and wider. The joining pins for '0' gauge are too big to fit in the ends of '027' track.
Your layout will be either all '027', or all '0' gauge track.
Larry