When seeking to acquire informed consent the default solution tends to be that you can obtain a written consent from each and every customer. This is of course perfectly fine, if it is manageable. But even  overcoming this task leaves the burden of gathering the consent documents and filing them, followed by ensuring the data is correct etc.

Remember, consent is just one of the ways in which processing data might be justified. Therefore, consider the processes that you are seeking consent to carry out, and look at alternative lawful bases.