Please don't worry, you really have no need to medically, although I can understand your concern given what you have been through with your husband and being the only living parent of a young child.
Whilst this does need to be checked out just to be on the safe side, it is extremely common to get a bit of endometrial proliferation and bleeding on hormone therapy.
This is simply the uterus doing what it has always done in the presence of those hormones, it is not pathological and really doesn't need to be feared as it so often is.
Normative data for postmenopausal endometrial thickness, with a cut off of 4mm, is based on women NOT taking hormone therapy. The system is simply not smart enough to distinguish between someone not taking any hormones, in which case 9mm would be more concerning, and someone whose endometrium is under estrogenic stimulation.
No normative data for endometrial thickness in women on hormone therapy have been agreed upon, however cutoffs of between 8 and 11mm have been proposed by various experts.
In your situation it is almost always benign and easily remedied by tweaking the progestogenic component, either increasing the dose or changing to a more potent progestogen such as the IUS or an oral progestin.