What about making a garden bed in part of the lawn and installing a woodchip path next to that? I love our woodchips paths and woodland beds in place of lawn out back. We also added a paver patio on sand that is easily removed if desired. We edged the 12x12 pavers with brick and it's neat and functional with a bistro set & bench. We added a few portable fountains and it's a fun place to hang out. Plus the hummingbirds adore the fountains.

Perhaps, the landlord dosen't want bare soil. Seeds are slow to get growing in summer unless you can keep the moist. Also, perennials take awhile to bloom and may not be fast enough for your landlord or you. I don't know if the mix of seeds you mentioned is going to be the look you want.

There are a lot of other groundcovers that could be planted the same day as you cover the grass. In fall you can add more. Then again in spring expanding the garden little by little.