Lynn, I am so sorry your last cycle didn't work. I was holding out so much hope for you
I don't presume to know exactly how you're feeling, but I think I'm kind of there right now. I'll be 39 in August so age is a factor for me too. After the BFN in cycle #2 our RE ran a ton of tests on me but it all came back o.k. There is nothing physically wrong with me. DH's SAs have all been right in the normal range for motility and quality. They did b/w on him, not sure what they ran exactly but it all came back clean. But, I don't ovulate without drugs. Even on Clomid I was lucky to get a few follies. Our RE said we have only a 1% chance of getting pregnant the old fashioned way.
From cycle #1, at 5 days, they had 2 perfect blasts to freeze so that is what I'm working on transferring now. DH and I didn't want to go with just 2 but the thaw rates at my clinic are about 95% so that's really good and they're pregnancy rates with frozens vs. fresh are the same.
I could have written where you said:
"it's a lot to invest... financially, physically and even more so, emotionally. Not sure I have it in me if the odds are against me b/c of age."
To answer your question, since you asked for input, I say YES do the FET with the 1 you have! This cycle has been a lot easier on me, it's very different than the fresh. I'm really hoping that doing something different will bring about a different result
Good Luck to you in whatever you decide to do. I'll be here cheering you on, we all will!!