Hey op, I'm 39 and have been trying three years with 2 failed ivf transfers and one spontaneous pregnancy that ended in missed miscarriage.
Obvs there's no magic pill, but you're absolutely right in thinking that to nourish yourself properly you will at the very least make your body more likely to receive a pregnancy. Looking after your general health and making sure you eat well will definitely help.
I've only just started proper supplement taking (I was just multivitamin and vitamin d with folic acid before, although I eat sort of healthily naturally). We didn't stop alcohol until 1.5 years in. I now stick to 2 teas a day with the occasional coffee as a treat, and a glass of wine very very rarely. I also gave up running :( I wasn't told to, but I honestly couldn't imagine all that impact helping anything.
It takes three months for eggs to mature into what gets ovulated, so it takes three months for any changes to take effect on egg quality.
As it's getting late, I'm trying anything now! I was already pretty much eating a Mediterranean diet, but am way more conscious about it now. Avoiding processed foods. Avoiding all toiletries that have bad rep on the Yuka app (things that contain endocrine disrupters, carcinogens, or things that can alter dna). Taking ubiquinol (ok yes, maybe it's unproven, but it also won't hurt. It's meant to give more power to mitochondrial processes. Older eggs have slower power supplies, so in my mind anything that helps cell mitochondria is good). A recent consultant shrugged his shoulders at it but said it wouldn't hurt. And it makes me feel like I'm helping, and I don't have much time left. That same consultant recommended me taking inofolic alpha (or rather, myoinsitol) I don't have pcos (who it's intended for) but he said it supports ovulation and egg quality and that it is a proven supplement. I haven't researched this myself, but might as well trust him, so ordered some.
If you want specifics on what I bought once you've done your own research I'm happy to share. There are threads specifically about certain supplements which I've found helpful. Oh also, a thread for those who are trying for their first child and are over 35. I'm on that and it's nice to discuss things with other women in the same boat.