Comfort classic allows stopovers up to 72 hours without a fee.
Check online if you find availability for the same fare bucket for your flights (Comfort fare buckets are A, S, W. A is the cheapest, S is usually around 150$ more expensive on my routes, W is the most expensive and usually over 1000$ more expensive on my routes; on airplanes which don’t offer Comfort class, the equivalent fare buckets in economy are A > M, S > B, W > Y).
Aeroflot website isn’t great at understanding stop over rules during booking. Call Aeroflot office in Moscow (number is in the footer of their website) to book. They have English speaking agents.