No you don't - you want what we call "conservatorship" over a child.
Guardianship is handled in probate court. You will be under strict judicial control. It's expensive and time consuming. Sometimes a case needs to go to probate court, but I usually try to avoid "guardianship" over a minor child.
"Guardianship" must be done for children about to reach 18 that cannot take care of themselves. Such as a child completely disabled in some way (mental or physical). The child is about to become an adult but they cannot make decisions for themselves like an adult would be expected to do.
The Texas Family Code controls "conservatorship" of minor children. A minor child is under the age of 18 in the State of Texas.
To discuss your options, talk to a family law attorney in your county.
I would look on www.avvo.com or the State Bar of Texas website for an attorney to help you.
Prices vary dramatically. So look around. Some attorneys offer a brief free consultation to see if they can help you. Some attorneys require that you come into their office and pay a fee to even meet with them. It is up to each individual attorney to determine their policy in this matter.