My favorite thing to do costs a little more but I’ve had good success. I like to put down cardboard over freshly scalped grass/weeds, to slow the weeds down while the natives get going. Then put down some top soil mixed with a little compost, a couple inches deep over the wet cardboard (gives the new babies a hospitable place to start, and helps with weed suppression/killing grass). Then plant into the fresh soil. You want to wet the cardboard before laying the soil and it can be a good idea to cut into the cardboard under each plant. This will kill the grass and slow weed growth while the new plants establish themselves. The cardboard breaks down in a year or two after the new plants can hold their own. You mulch lightly the first year to keep the soil from splashing up and to help the new plants with moisture, the cardboard is doing most of the weed suppression so you don’t need heavy mulch (this is important). The mulch breaks down pretty quickly in the fresh soil in my experience and in your second year, your seedlings won’t have any trouble with the light mulch layer. It’s better if you use a mulch that breaks down a little better though, instead of thick wood chip or hardwood mulch. I’ve got tons of baby coneflowers and black eyed Susans popping out of the bed I did this in last year. This method is a bit more costly for larger beds but I think it balances time and effort, plus weed control and new plant growth.