For the first 90 days you don't want a lot of décor - minimalist is better - in case the snake arrives sick or with mites, so there's less to sanitize.
Otherwise, soft fake plants with no loops for your snake to get stuck in, or sharp edges/protruding wires to scratch him, are fine. Craft stores carry them for half the price you'd find at a pet store and many have the same SKU's.