Morning starshine & Welcome. There are a couple of us ladies who ve had treatment at Serum with donor eggs. I had a full donor egg cycle back in September and am almost 28w pregnant with a little girl (upon first attempt, and have 3 frosties too), and another of us has gone for the embryo adoption route and been lucky on her 2nd attempt. There are several others on this thread who have been either successful on this route or are trying, thru clinics in Spain, Greece and I think Cyprus
Serum are an absolutely fantastic clinic, they have great success rates, their customer service is excellent (from Medical Director/Founder to the Consultants thru to all the reception staff turn queries round often same day). You will be very well looked after.
Once you ve had the initial phone assessment or alternatively have gone over for this, its really a very quick turnaround. I had my initial phone consult on 24th Jul last year, and I was in active treatment by the end of August to grow womb lining. So really you ll only need to have a cycle in between, or if timing is right, you can jump in almost straight away. You may be aware that sometimes (depending on fertility history) they suggest/recommend having a hysteroscopy, and usually suggest an aquascan regardless. If hysteroscopy this can delay things a bit, but aquascan can be done in UK or at Serum just prior to treatment (has to be done early in cycle - after period and before day 12 is usually suggested). Obviously you needn't have either but it will probably be suggested in a bid to maximise your chances.
In terms of donors being found, this is almost instant. You give your list of preferences and the clinic will match them. Embryo adoption is cheaper - and thus sometimes (but not always) less scope for matching as embies are already developed so the clinic would get the best possible match on say hair colour/eye colour preferences. These are defrosted (in pairs) and usually both are suggested to transfer.
Full donor egg cycle is a 2K more expensive (plus storage costs for other embryos) but you can be a little more specific in preferences and hopefully would get at least 1/2 more attempts with FETs, although that cannot be guaranteed. I got 5 top AA blasts in total, had 2 transferred and 1 took. Both methods have similar success rates.
In terms of starting donor egg cycle. You usually start on day 2/3, you are asked to get scanned here at around day 10 to check that your lining is coming up and then transfer mid cycle ish. So I think I started the lining protocol on the 30th August and had the transfer on 14th September. This will vary depending on your donor's response to stimms.
Where are you based in UK? Hopefully you ll have a local clinic that can perform the private scan and somewhere fairly close by for aqua scan if needed or decided. Are you doing this as a solo mama?
The AMH is a major pain in the arse. Mine was in a very similar place at the same age as you, and I expect its non existent now. I'm 41.5. Serum do offer own egg protocols for natural or natural supported cycles for poor responding women, but for both of these they only look to get that 1 golden egg, so it is a total gamble, so going straight to donor treatment I think is your best shot
Let me know if can be of further help. Good luck!