If you want low to the ground, you could do a mixture of ajuga and sedum. Ajuga can get in the lawn if it loves your property, but sedums rarely would. They can both handle your full sun. Regarding the junipers, I'm not sure that they would really "grow around" the spireas. I think they'd eventually end up competing and overcrowding each other.

Pachysandra is my workhorse for deep shade here in the mid-Atlantic. It spreads great, it's evergreen, it doesn't mind having NO irrigation, it's self-limiting (as it fries in too much sun), and it doesn't try to climb and strangle everything. The neighbors have vinca minor in deep shade. It's doing fine but isn't the same thick mat as the pachysandra. Ajuga does well with no irrigation. Hardy ferns are fine, but they don't spread all that well for me. Hostas will grow that densely, too. So will hardy geranium--the native type is what I grew in NM without any irrigation in a natural low spot. It won't take super-deep shade. In New Mexico, my go-to ground cover was English Ivy. It fried like an egg on a hot plate in the sun, and the near-desert conditions meant I could keep it in bounds. Not in your zone, though. It'd eat everything. (In NM, I'd go after anything that was invasive in other states but not where I lived. That meant it'd likely be a survivor but not dangerously aggressive!) I had some invasive wild rose that would grow in shade there, too, and some perennial sweet pea there. Give up on the wildflowers. They won't do in deep shade.

English ivy is EXTREMELY invasive and highly discouraged. Try Boston ivy (Parthenocissus tricuspidata) or Virginia creeper (Parthenocissus quinquefolia). Most native shrubs will grow vigorously. Crabapple (Malus fusca), and several varieties of blueberries, salmonberries, some varieties of currents, amelanchier, elderberry, high-bush cranberry, kinnikinnick, and bunchberry (Cornus Canadensis) are native to your area. Look for a local native plants book, or my bible: Plants of the Pacific Northwest Coast, Washington, Oregon, BC, and Alaska by Pojar & MacKinninon. Good Luck!

Any good garden centre that sells lawn seed should have small bags of white and red clover right beside it. It shouldn't be expensive either. I strongly recommend the white clover it doesn't grow as high as the red and it grows slower. Unless of course you are into making tea then red clover is right on. Buy a second bag and spread it on your lawn out back too... It is a natural fertalizer and will make your lawn look greener all summer long. Try and keep it an even spread through your lawn otherwise your lawn will start to look patchy. The below stolen from another website 1. It stays a luscious green all summer, without being irrigated profusely (i.e., it's drought-tolerant). 2. It is free of weeds, obviating the need to apply herbicides. Your carpet competes so well for growing space that the competition is choked out. 3. It doesn't need to be fertilized. 4. It is also relatively pest-free, so that you don't have to bother spraying pesticides on it. 5. It aerates the soil on its own, so that you don't have to worry about counteracting soil compaction. 6. It is soft to walk on. 7. It attracts beneficial insects, including honeybees. 8. It rarely has to be mowed. 9. It doesn't suffer the discoloration from dog urine known as "dog spots." And if, despite all these benefits, you should ever want to replace it with a different kind of green carpet, it helps you to do so by improving the soil on its watch. Its ability to aerate the soil and pump nitrogen into it means that succeeding generations of plants using that soil will be better off. Thats not a description of grass.... thats white clover. We have gotten too use to the golf greens me thinks. I'm a firm supporter of alternative ground cover. Grass has its place for areas of high traffic... I've done ground cover with clover and bugleweed mix and it looks really neat together... Just a thought. Diversity is common place in this world. And if they do get tall over a long period of time both can be mowed no problem. But they are both way slower growers then grass.