What is the next closest fund to FXAIX that tracks S&P 500 and is available on Fidelity?

My wife wants to give me some money to invest in my account and I want to keep it separate from the funds that I’m currently invested in. My money is in FXAIX and she wants to be in the S&P 500. I tried VOO, but it only trades in stock quantities not dollar amounts, I don’t like that. What would be the next closest thing that is more similar to how FXAIX works?