I am a Houston Realtor. I helped my clients with this information in the past. Have you contacted your previous realtor that helped you buy the home? Call me if you want a little help or a few pointers.
Hope your week is terrific, Kathleen
Sale prices are not recorded in Texas, so no public access. Loans are recorded and you can access this information at the county court house. That would not be the full price, but a starting point. Don't use Zillow or other web based "value programs" as they only access the county appraisal values which are not as accurate as your local Realtor pulling up sold prices from the local MLS.
Contact a Realtor to access the recent solds comparble to your home for your tax protest. Typically no charge for this. Good luck on your protest!!
Hope this helps, Dc.