You only need a notary. He/she will draw it up. I have known them draw attention to things which may be potentially a problem, and to advise.
Even if you use a lawyer, the document can only be authorised by a notary. So you would be paying twice for the same thing of you use a lawyer. Of course, if it is very complicated you may think a lawyer is a good idea,
I amd my family have made several Wills, all drawn up by notaries, over the past 25+ years without any problems. For son, who has little Spanish, they even provided a copy in English too.