There are ways to at-home test the soil composition in different parts of your yard through wetting, shaping, and examining it but if youre in the US you can also just check the USDA Web soil survey to check your area's soil. If you want to really get into it, you can send off a soil sample for testing to know if you're lacking/overboard on any nutrients or need to alter the pH - your local university extension should either process these themselves or have a list of local places to send them.
Specific location means SPECIFIC! Look for plants that grow in the elevation and specific climate youre in - Oregon (for example) has a ton of different habitats, and what thrives in the eastern desert is very different than what will thrive in the temperate rainforest or cool coastal areas. Check native plant guides, or even just go on a walk to some nearby parks and take pictures of what you like that grows well where you are to ID later on - apps like iNaturalist can help with this but always doublecheck info and don't assume its native just bc its in a park. You can also call or email your local Master Gardener's group for specific info, advice, and resources.
Think about your big picture for the yard - groundcover that needs plenty of shade and canopy overhead will be amazing in a fruit tree guild, or selection of native flowers, bushes, and small trees building layers above it. It'll do horribly in full sun as the main cover for your lawn. Do you need wide access paths for wheelchairs or carts? Do you want to grow food for you, or the birds, or neither? More layers means more microclimates - cooler, wetter areas and areas you can leave open, hot, and sunny.
On that note, diversity builds resilience. Choose different species (or varieties of the same species) that are hardy against different things. A lawn with one species can easily be wiped out in severe or long-lasting weather - a lawn with 3 or 4 species, some hardy against drought and others flooding or disease, means 1 event won't wipe out everything and the others can provide some shelter for the plants that were hit hardest. Recovering in a field of dead grass, holding no moisture and all the heat that hits it, is harder than recovery in a field of other living things to moderate temperature and some of the weather. Diverse plantings also brings in more, and more diverse, insects and animals - some of which will be predators for problem pests, or food for local bird populations.
Replacing a lawn in a short period of time is VERY expensive and energy-intensive. But - depending on your area's rules - you can do it slowly and progressively, a bit at a time. Everything that follows assumes you've checked your neighborhood/city rules and called 811 to make sure there's no gas or power lines where you're sticking a shovel. Some people even make little info signs or something if they're tarping/putting cardboard over half their yard, so nosy neighbors understand its temporary.
Lasagna cardboard methods can be used to smother the grass. Tarps can be used in spring-summer to kill turf with shade and heat, especially if there's a lot of noxious weeds in it. Woodchips (NOT rubber) can be put down to slowly kill most of the grass while breaking down in place, and can be delivered cheaply with Chipdrop.
Free bulbs, flowers, bushes and trees can be found in local gardening groups, buy nothing groups, seed and scion sharing events hosted by groups like the Agrarian Sharing Network, or groups like Friends of Trees who give away free native trees and advice on how to plant them. Many farmers will post on craigslist when they have too much compost to deal with, and you can get free aged manure or compost as well as woodchips this way. Just be cautious of putting UNAGED manure directly onto young plants (itll "burn" their roots) or things you intend to eat. There are even groups that (with permission!!!) go harvest native plants from construction sites before theyre demolished!
Once established, a group of native plants (in the right place right soil right conditions) should largely take care of themselves beyond basic maintenance to keep them the size you want and keep them watered in major droughts. The first year is the most crucial in keeping newly germinating seeds, seedlings, bushes and trees watered. Bushes and trees might need help for another year or two depending on the type, and most things need some help during the increasingly severe weather we're getting, but a lawn replaced w native plants done RIGHT is a lot less work in the long run. It is definitely a big effort up front, whether done slowly or all at once, but every little bit is a piece of rebuilt habitat for insects, pollinators, birds, snakes, and more - and one step towards people seeing & normalizing using these big empty spaces for growing food and habitat and LIFE again
