Depends on you plant spacing, you could use a weed barrier but when you get done, you probably wished you pulled weeds. Costco has it in the spring. Grey in color. Compost might be good to mix in with your existing soil, make the soil more friable, easier to pull weeds. What kind of mulch did you bring in the had different kinds of weeds? Chipper mulch might be the best kind, 2" deep, should keep the weeds down. Call an arborist and see if they are trimming trees in your area, it could be cheaper then buying bags at a big box.

Here is a link that might be useful: Propagating Perennials