The average American landscaper LOVES to plop a compact, small (for the space) shrub, perennial or annual in a sea of wood or stone mulch. Employing organic mulches (I recommend organic over stone as they feed the soil and plant as they break down) is an excellent sustainable practice. If you choose to employ it, please use a red dyed or other natural color (like black) organic mulch. There are a number of excellent benefits to employing an organic mulch, typically available at a garden center near you, but I want you to consider another sustainable option: planting to the hilt.
No matter what you do, you should aim to cover the ground with something. Nature in general hates bare earth. That is what weeds do: quickly cover the ground to hold it in place against erosion. But why only plop a plant here and there, with nothing between but dead, ground up trees or wood pallets to connect the dots? If that is your aesthetic, cool beans, but as I have hinted for the past several sentences maybe consider something else.
Consider designing your space using mulches as a temporary part of the bed in its immature state rather than still covering the majority of square footage when the planting bed is “mature.” Look at a meadow, which is somewhat akin to your average flower border. See any wood mulch there? Nope. Every square inch is covered by a diverse array of leaves, flowers and importantly root systems. Meadows grow in layers, with different plants fulfilling different roles and niches below as above ground. You get the same benefits such as weed suppression, temperature modulation, moisture retention, soil nutrition, etc wood mulches provide, with the bonus of exploding beauty.
Flower beds planted to the hilt for four seasons of interest are more interesting and more resilient. Think of all those Better Homes and Garden or Pinterest pics you see. They are almost always packed frame edge to frame edge with plants. We instinctively respond to such design. Happy Planting!