If you can afford plants, you can afford to have someone else care for them. Click to place a single tile of Floor in a grid space. Click and drag to place tile in a larger area. Control-click will erase a tile. Various floor styles are available to the discerning Sim.
Linoleum works best for the kitchen.
Cheap carpet is a good start anywhere else-especially since when you replace it, you get refunded for the original purchase. All of your indoor spaces should have flooring of some sort. Certain floor tiles are obviously for outdoor use-the concrete and cement tiles make front walks. Other outdoor tiles work well to create patios or basketball courts. There are even some street-like tiles to play with.