Soothful is a rare word in English language, and its synonyms are also limited. However, some words that could be used in place of 'soothful' are words like soothing, comforting, calming, peaceful, and relaxing. These words convey a sense of tranquility, quietness, and calming effect. For instance, if a person is seeking a sense of peace or comfort in an environment, one could say, "the atmosphere is so soothing here," instead of "the atmosphere is soothful." Similarly, one could use "calming" instead of "soothful" when describing the effects of a spa or aromatherapy. Altogether, while the options for synonyms of 'soothful' may be limited, there are some suitable alternatives that can be used in a similar context.