c# Form 스타일 None 일때에도 폼을 늘릴수 있습니다.
        private const int
         HTLEFT = 10,
         HTRIGHT = 11,
         HTTOP = 12,
         HTTOPLEFT = 13,
         HTTOPRIGHT = 14,
         HTBOTTOM = 15,
         HTBOTTOMLEFT = 16,
         HTBOTTOMRIGHT = 17;
        const int _ = 10; // you can rename this variable if you like
        Rectangle Top { get { return new Rectangle(0, 0, this.ClientSize.Width, _); } }
        Rectangle Left { get { return new Rectangle(0, 0, _, this.ClientSize.Height); } }
        Rectangle Bottom { get { return new Rectangle(0, this.ClientSize.Height - _, this.ClientSize.Width, _); } }
        Rectangle Right { get { return new Rectangle(this.ClientSize.Width - _, 0, _, this.ClientSize.Height); } }
        Rectangle TopLeft { get { return new Rectangle(0, 0, _, _); } }
        Rectangle TopRight { get { return new Rectangle(this.ClientSize.Width - _, 0, _, _); } }
        Rectangle BottomLeft { get { return new Rectangle(0, this.ClientSize.Height - _, _, _); } }
        Rectangle BottomRight { get { return new Rectangle(this.ClientSize.Width - _, this.ClientSize.Height - _, _, _); } }
        protected override void WndProc(ref Message message)
        {
            base.WndProc(ref message);
            if (message.Msg == 0x84) // WM_NCHITTEST
            {
                var cursor = this.PointToClient(Cursor.Position);
                if (TopLeft.Contains(cursor)) message.Result = (IntPtr)HTTOPLEFT;
                else if (TopRight.Contains(cursor)) message.Result = (IntPtr)HTTOPRIGHT;
                else if (BottomLeft.Contains(cursor)) message.Result = (IntPtr)HTBOTTOMLEFT;
                else if (BottomRight.Contains(cursor)) message.Result = (IntPtr)HTBOTTOMRIGHT;
                else if (Top.Contains(cursor)) message.Result = (IntPtr)HTTOP;
                else if (Left.Contains(cursor)) message.Result = (IntPtr)HTLEFT;
                else if (Right.Contains(cursor)) message.Result = (IntPtr)HTRIGHT;
                else if (Bottom.Contains(cursor)) message.Result = (IntPtr)HTBOTTOM;
            }
        }
운영하는 c# 소스코드에 그대로 복사해서 넣기만 하면 자동으로 처리됩니다.
저는 위의 코드보다 아래코드가 바로 되어서 아래 코드를 이용하고 있습니다.


this.FormBorderStyle, DoubleBuffered, SetStyle 부분은 삭제를 하더라도 잘 돌아가더군요.
참조: https://stackoverflow.com/questions/2575216/how-to-move-and-resize-a-form-without-a-border
