Hi! I totally don't think you need a dress form for well fitting garments for several reasons. A, The likelihood that you will find a dress form that is the EXACT dimensions of your body is highly unlikely. B, Dress form fitting doesn't take into account movement, so you need to make a toile or some such to see if you can actually MOVE etc. Often fit issues only come to light when you are no longer standing stock still. C, Things like armhole depth, neck hole shaping and hem lengths may look fine on a dress form, but may be rubbish when the garment is actually on your body.
I have a dress form, but I only ever use it to show off finish garments and take photos, or to put something half finished on which I find more motivating to continue than putting it down on my sewing table. All the best!