Data Controls :: How To Add TextBox To GridView Column

I am trying to achive the following. 

I have created a form that populates a Gridview with 7 coloumns via 3 DDL's. This is working as intended. I however need to implement Writeback to two coloums on the table while keeping 5 of them read only.

Below is the codebehind

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

[Code] ....