In their paper on Progestogens and Endometrial protection, (Tools for Clinicians) the British Menopause Society say this:
"Earlier studies have reported that desogestrel 150 micrograms is effective as the progestogen component
of HRT with no increase in the risk of endometrial hyperplasia.33-34 There is lack of evidence on the use of
desogestrel 75 micrograms as the progestogen component of HRT. If desogestrel 75 micrograms is used
as contraception in women receiving HRT, it would be recommended to add further progestogen (e.g.
Utrogestan 100 mg daily or 200 mg for 12 days a month) to provide adequate endometrial protection."
So one option which would be off-licence, would be to take 2 Cerazette along with the oestrogen component of HRT, as per the above - in consultation with your specialist. There have been women on this forum who have been properly prescribed this combination and this dose.
Some women find that taking additional progestogen as part of HRT along with the mini-pill gives them too high a dose of progestogen, if they are sensitive to the side effects.
Re irregular bleeding on HRT - this depends on your underlying cycle ie your stage of menopause, the condition of your uterus (eg any fibroids or polyps), and the dose of oestrogen and progesterone ie type and dose of HRT. I never got any abnormal bleeding after starting HRT, for the first few years because I started in late peri-menopause and my cycle was very infrequent (have had a couple of other eposides of spotting which have been investigated, but nothing to worry about).
Hurdity x