Suggest that it is worth withholding any other treatment until you have had an assessment, which is likely to be soon. The scan findings could be a polyp, which are common and not serious. Also, the measurement very much depends on if you are still perimenopausal or postmenopausal, and what HRT regimen you were using.
I would not recommend buying hormone treatment online, including norethisterone--it can have side effects, and if used in the dose that is recommended to bring on a bleed, or stop bleeding, it is associated with an increased risk of deep vein blood clot.
It would be very unlikely that there is any serious findings, but suggest just waiting at the moment.