There are several ISOs that are a good fit with care companies. ISO 9001 is the Standard for quality and can help you to deliver high quality care to your service-users.
ISO 45001 is also very relevant as it is the Standard for occupational health & safety, helping you to manage and control risks to keep your employees safe.
Another ISO you may want to consider is ISO 27001. This is the Standard for information security management and can implement processes to keep service-user data confidential.