When to stop trying?

Hi everyone ❤️ I have a 3.5 yr old son who is my absolutely everything. He was born after 3 ectopics, 1 early loss & 2 rounds of IVF so I realise how lucky I am to have him. I'm completely infertile so a potential 2nd child was always going to have to be IVF conceived. We had another FET in March this year which sadly ended in a chemical pregnancy. We then paid our clinic for another round & meds which have just sat there. I feel like every month I've been putting it off as we had events etc. Now I'm at the stage we can do it I'm just not sure I want to. I feel so guilty for not being 100% all in to give my son a potential sibling. Would it be so bad to just have one child? I worry for his childhood & him being lonely. I'm also now thinking about my age 36 & my partner is nearly 41, we're already "old" parents to my son. I feel like I've finally got a little bit of me back after this summer & letting my hair down. I'm so torn between having another round, another potential fail 😭 or just throwing all my energy into giving my son the best possible childhood as one & being the best version of me. TIA xx