Do you have room on your trailer for hauling mulch 1-3 yards at a time? I'm small too, and only have one trailer running. So I only do mulch on days I'm not mowing since there isnt' room for both. You should find a couple of bulk soil providers, its not luck, they are in the yellow pages, ask for their contractor price and get it by the scoop/yard.
Another tip that I've figured out when just getting started and trying to improve my quoting. Keep notes and pictures of the jobs you do about how long and how difficult the job was. I refer to my notes/log next time I'm quoting.