Need Advice (long note, child mentioned, late pregnancy loss mentioned)

Im coming to this board for some sound advice. I have not posted much before but I lurk very often. Can you offer any suggestions on what would be the next steps to take in order to give a sibling to our child? I still have some hope for using my own eggs but Im not opposed to a gestational carrier.

My detailed history is below but in a nutshell; I have been pregnant 3 times (1 chemical, 1 loss at 20 weeks, and 1 live birth at 28 weeks). The 2 viable pregnancies I had were right after a failed IVF cycles (both times my estrogen levels were in the 3,500+ range). For some reason, IVFs dont work (Ive done 6 already) and my gut theory is that I have some sort of a lining issue. I cant prove it but I just have this suspicious feeling. I even had an endometrial function test and that came back normal. Ive had immune testing done also and came back normal except MTHFR Heterozygous, which is an easy fix by taking Folbee tablets.

Im 40.9 yrs old and have been doing this for 6 years now and I am very grateful to have one live birth but Im not ready to give up on giving my DD a sibling. I dont know what to do at this stage. This emotional ride has taken a toll on me and I keep reliving the horrible experience of giving birth to my precious boy and how badly I yearn to hold him in my arms again. I keep thinking only if I did this or that, my precious son would be here. Sorry to be a downer and Im hoping to get some support and suggestions here.

Me - 40 yrs old (elevated prolactin levels controlled by meds, elevated CD3 E2 levels, fibroid history resolved by myomectomy surgery)
Hubby - 41 yrs old (no issues)

My History and treatments:
TTC since 2006
Multiple natural IUIs, Clomid and FSH IUIs BFN
Hysteroscopy done (age 37) polyp removed
FSH IUI (age 37) chemical pregnancy
IVF #1 (age 37) 1 blast and murela transferred BFN

Natural IUI (age 37) BFP all was going great until my water broke at 20 weeks. Our precious healthy chromosomally normal baby boy went to heaven too soon. Spent time grieving and to heal my body. Likely cause of PROM was degenerating fibroids.

Abdominal myomectomy done to remove fibroids and the healing process continues

IVF#2 (age 38) 3 day 3 embies transferred BFN

IVF #3 at Cornell (age 38) - transferred 4 day 3 embies BFN

Taking a mental break (age 38) BFP all went well until diagnosed with an incompetent cervix, most likely due to weak uterus from the myomectomy or just plain old aging process. Delivered prematurely at 28 weeks but my baby girl is a fighter and came home after a 70 day hospital stay.

IVF #4 (age 39) at a local clinic 2 day 3 embies transferred BFN

Estrogen Priming (age 39) - - took Estrace on CD 2 21 and provera on CD 21-25. Did this for 2 months in hopes to prime the uterus and possibly repeat the scenario of getting pregnant after failed IVFs. Goal was to do IUI to get preggy naturally. This attempt backfired as I developed a huge cyst that took 3 cycles to go away. Overall, I lost 6 months with this attempt.

IVF #5 (age 40) at BIVF all 4 embies were frozen since I couldnt make it to the transfer due to being ill.

Endometrial Function Test (age 40) came back normal

FET #1 (age 40) transferred 4 embies but sadly it is a BFN