Age Gaps: Parents of Multiples

My husband and I are a blended family. He had two, 15 yo boy and 10 yo girl. I had one 12 yo boy. We recently (March 2021) gave birth to our own. He’s 38 and I’m 32. We want another one so that our 3 month old son doesn’t grow up alone. The older kids will be....well older and out lol. I don’t want to wait too long due to our ages but don’t want to be a health risk. There’s also no guarantee that I’ll get pregnant right away. What’s a good age gap to try again?