Door thresholds, uneven floors etc

OK fitted the new floor, made it nice and level, one joist at the end was a bit low. However now when trying to fit the threshold bar at the door the old floor I'm meeting with is lower at one end. The expansion gap between the two is a bit wider than I'd like also. It's carpet on the old side, so I'm a bit unsure ass to the best solution and am considerinhg trying to make something to custom fit as the standrad carpet/threshold bars don't seem suitable.

Any thoughts?

Im not a tradesman but... I've used nice hardwood thresholds to great effect to get different level floors to look well finished.

Thick tiles to low varnished floorboards....carpet to laminate...you name it...a nicely finished threshold the same width as the door in a suitable wood always looks nice. ..IMHO. I much prefer them to the metal joiners even for carpet to carpet..so maybe Im biased.

They are easy to make as well if you can run a rebate with a power plane or router. Before I had my power plane I even went to the trouble of attacking one with a drill and chisel..

Ive made all mine from bits my dad has had lying about...he is an old joiner so that was lucky for me.

Im sure the experts on here will have a better idea!