Budgeting Around My Partner’s Irregular Income and Our New Baby Expenses

My partner is a freelancer whose monthly income swings between $1,200 and $3,500, which makes our budgeting unpredictable. We recently had a baby, so our expenses jumped with diapers, formula, and doctor visits. I work a steady job bringing in $2,500 monthly, but trying to cover all the baby-related costs plus rent and bills is stressing me out. We’ve tried setting aside a percentage of the higher-income months into a savings buffer, but it’s tough to know how much is enough or when to tap into it. I’m hoping to find a better way to balance our fluctuating income with fixed expenses and growing baby costs without constantly feeling behind. Has anyone dealt with irregular income alongside a new family member and found a budgeting method that actually works? How do you decide how much to save versus spend when you can’t predict your partner’s monthly earnings? Any strategies for managing those unpredictable months while still planning for future expenses?