@Mod-Nomsie has said what I was thinking.
I'm not an ivf mum but my son was nearly 2 when my twins were born. They were 4 weeks prem and spent 2 weeks in special care. I had gestational diabetes and one twin stopped growing.
Twins are great, they are amazing and unique, but honestly if I could choose I would have only had one at a time (naturally conceived so i didn't get a choice). My son has missed out so much because of how much time and attention the twins needed. And the twins don't get much one-on-one time either because they are kind of treated as a single entity.
My advice is to think carefully about what is best for you and your family emotionally, rather than focusing on the financial and logistical side.
Sorry, I don't mean to be a downer! There are plenty of positives which you will no doubt hear but I feel in your situation it is important to hear some of the negatives to assist in your decision.
All the best to you and I hope you are blessed with a beautiful healthy baby or babies either way