Aayla - so sorry to hear that you are likely becoming resistant to the letrozole. I know it's hard to handle, especially because IVF is starting to become more of a reality.
I'm going to give you my experience with weight and IVF for you to do with as you please. I know everyone is very different, but I did find it helpful to hear how others responded to get a good idea of what I wanted to do. Anyway, my BMI was around 36 at the start of my last round and one of my doctors still blamed my failed cycle almost solely on my weight - saying my egg quality was so horrible that none of the embryos divided correctly because of my weight (despite none of my doctors expressing any concern what so ever before the cycle began). Now there's no way they actually know that's the reason and I have a lot of other concerns about how my cycle was handled that in my opinion could have affected stuff more.
Regardless, it wasn't a good feeling to have that thrown in my face after a failed cycle and spending so much money. It made me feel like an idiot for proceeding without losing even more weight first, despite me thinking my age was more important (now to be honest I don't know what to think - because I wish I would have waited a few months to get down just a bit more weight). Now, it's a fine balance between age (which in my opinion is more important) and weight (which is really only a decent indicator of issues you might face - such as egg quality and implantation issues that aren't exactly measurable). So you can't wait forever to lose the weight; it's just not realistic. But you do need to be prepared that even hitting the 38 BMI that the cycle can fail because of weight issues or really any unknown issues. My doctors said under 33 is ideal and in the UK they like it under 30 (again it varies so much by person and you never know until you go through your cycle).
I also wish I would have been more realistic when I approached IVF and realized that you are looking more at 2-5 cycles of IVF. Ladies do get pregnant on the first cycle, but it's not hugely common given our age. So be prepared to spend closer to $20,000-$30,000 if it's $10,000 per cycle. We bought a 2 cycle plan and I regret it even now. I wish we would have bought a 3 cycle plan that came with a reimbursement if I wasn't pregnant. It was about $15,000 more and I think would have been worth the reassurance. I went back and forth on it when decided what we wanted to pay upfront. I know they do everything very different in Canada though and it's great that yours are cheaper per cycle to begin with!
Anyway, I think it's awesome you are going to proceed with IVF and know you can reach your goals. You have already been so motivated and have been doing great. I'm really excited for you. Just be prepared for it to potentially take some time even with IVF. It's so hard not to get discouraged along the way, but just keep pushing forward!