You say "thin enough to mach an Ego", then say "about the width of regular DC tank". This is contradictory.
As far as I know, there are only two carto tanks to match the width of an Ego style battery.
The
2.5ml ego carto tank and the
3.5ml DCT, both are obviously for xl cartos only. ( links are examples only )
I don't know if you could cut down the ego tank, but if you are very careful, you could cut down the DCT.
I say very careful, because the plastic on the DCT is pretty thin. I don't think you are going to find a vendor
carrying anything that short because it wouldn't leave you very much juice capacity.
If you don't like the dual coils, there are plenty of vendors who carry
single coil xl cartos.