When you get the chat button simply swipe up, this will reveal a bubble message icon instead.
Click that and another screen will come with 'To type a name, phone number' at the top. At the end of that line there is a 10 dot icon, click on that to reveal a keyboard icon.
Type your message.
You can't get rid of chat AFAIK.
If you don't like the stock android messenger you could install one of the custom apps on Playstore like SMS Organiser by Microsoft.