If you're timid, I think it's better to book through text with an independent and have a one-on-one meeting experience. If you inform the lady of your concerns, she will do her best to make the situation less stressful and awkward for you. They're experts, the majority anyway, at human interactions.
By the way, I’ve never been to a spa but I can imagine it being more stressful than a one-on-one. Definitely more people involved