Do I need a lawyer to set up a Will?

No, that lawyer is as wrong as wrong can be. ONLY a properly executed and witnessed will can control what happens to your assets after death--nothing else, no oral expression of your wishes, no writings or letters or documents that are not wills, matter. In your state, to have a valid will, your signing of it must be witnessed by two witnesses, both of whom then sign the will, too. Without a will, the assets will pass by intestate succession (the rules for who gets what when there is no will), with no input from you.
You are not required to have a will, but are strongly encouraged to have one; the lawyer can make sure that the will is properly signed/witnessed *and* that it is written to fully accomplish what you want. Besides leaving your assets to your son, you may wish to have a legal guardian for him, if you pass before he turns 18; you may wish to put money in a trust for him, to be doled out according to rules or guidelines you set up for his education and basic support, and not possibly have a young, still-immature man come into a lot of assets without any guidance or control over what he does with them.
You may wish to make your accounts transfer on death or payable on death (TOD or POD) to your son, they go to him immediately on your passing, outside of probate. You may wish put him on the title of certain other assets, for the same reason. An attorney can advise you as to your options and how to best effectuate what you want.