Whatever you do, as TFB has intimated, don't 'should'! 'Could' is much better, because it opens it up to the listener that it's something they can decide to take up (informed choice), rather than being prescribed a course of action, which no-one likes 'Shoulding' also implies that the person must come into line with the values of the speaker, and that's why 'shoulds' sit so badly with people, because we all come from such different value bases, and 'should-ing' someone tells them that you think their values are wrong, instead of letting them evaluate which values need adjusting to achieve a desireable goal.
Make sense? You'll get so much further by changing your language, because when you choose your language carefully you are automatically changing your approach to a more considerate one that cares about the person you're speaking to