If you want an Advocate for you during Labour, I'd suggest you get a doula. I'm in a similar boat to you and am weighing up the same options. I'm a pretty confident person generally and have never needed anyone to advocate on my behalf. However when I was in labour I was in a fair bit of "pain" and was really tired. It affected my ability to think straight. It was then that the Doula became the best $$ I have ever spent.

A student midwife may not necessarily be a good Advocate for you. It really depends on their previous study and personal history. If they are a mature age person that has kids, they might be able to perform that role but I wouldn't necessarily feel comfortable with an 18 year old first year despite their best intentions.

With our Doula I didn't feel 'crowded' at all. She was very good at staying in the background and supporting us when needed.

Hope this helps.