Email has been about for most of our lives now and we have become used to it. However email is not secure which is something that I am always reminding people about. In the early days we were careful to never send sensitive information especially anything about our bank and yet this has become common now. My advice is to never send your bank details and expecially credit card information by unsecured email.
There are better options than email for secure transmission. Messaging services typically use end to end encryption and can encrypt messages when stored. These are useful when communicating with known contacts and are great collaboration tools. Web forms and chat used by commercial service providers should also provide more security than sending your personal details unencrypted. Check to make sure that the site is showing https:// before the URL.
There are secure email services available now and these should definitely be used if you are sending sensitive information between organisations. However they usually require that both the sender and recipient have the same solution available. The other option is to protect any documents that you are attaching to the email and provide the password separately (e.g. by text). there are also some draw-backs of this approach because many organisations now block encrypted attachements.
The other option and this is could be the best in some situations is to share documents that are managed with a cloud service. Cloud services typically provide encryption at rest and the better ones now have the option of end to end encryption with you having the key. Your password manager can be valuable for storing the encryption key. Cloud services have options for sharing a document securely that you might suit your need.