First, unless you have a very good reason, use Content Controls rather than legacy formfields.

You can put your Content Controls in a Table (even a single-cell borderless table).

• Create a Form Using Word Content Controls by Greg Maxey
• Making Forms with Microsoft Word

Content Controls were introduced in 2006 to replace legacy formfields.

You can use the Group Content Control to limit editing.
You can use the Editing Restriction of No Changes, with exceptions, if you want something stronger.