2 year old twins, thinking about trying for another baby...?

Hey guys! I have 2 year old twin boys. I have fertility issues and it took me five years to conceive them, two of those years on fertility meds. Me and my husband are thinking about trying for another baby since it took us so long to conceive our twins. If you have twins and another child after them, how did you know it was the right time to have another child? How is it adjusting from just the twins to twins plus another baby? Thanks in advance! 💙