Hi ancient runner
I agree with the others - you have nothing to lose - the systemic HRT will boost your basal oestrogen levels and the local oestrogen will give that additional support to your vaginal/bladder areas where you need it most.
Do I gather you have an Estring as well as Vagifem? Once you start systemic HRT and are settled on this then you are unlikely to need both of these I expect.
Also to ask which type of Femoston? Is it the conti variety or the cyclical - to induce a bleed? If the former, you might want to start the latter ( unless the thought of bleeding is total anathema) just to see if you are OK with the oestrogen part separate from the progestogen.
All vaginal problems take a while to sort out - but if you are suffering flushes and sweats then systemic HRT should sort these out within days or at the most a couple of weeks.
Let us know how you get on

Hurdity x