“Can I bring someone with me for support during a mediation?”
Where you have a legal representative you should certainly bring them with you to provide private advice. There is no objection in principle to bringing other people but, like everyone else, they must sign the confidentiality schedule attached to the main mediation agreement. Bear in mind that if the number of people accompanying you outnumbers those with the other participant, they may feel disadvantaged and be less inclined to persevere when negotiations become difficult. The fewer people who come with you, the better.
A person who certainly should attend with you is anyone whose authority is needed for you to sign a Settlement Agreement. Waiting until the next day to obtain that authority frequently causes the oral agreement to unravel, wasting the effort and expense of the mediation.