If all you're doing is transferring account ownership then why wouldn't you just stay the same, just not be the account owner?
You'll need to complete a Change of Ownership which can be completed over the phone in most cases. You can find out all you need to know with transferring your account to someone else as well as moving your number to a different account here: Transfer account or line ownership .
What plan do you currently have?
Are you and whomever you are changing ownership over to aware of the cost of your plan may not stay the same (depending on what plan you are on).
If you have a T-Mobile ONE Plan you bought at a promotional rate of 4 lines for $100 dollars.... the new owner will not inherit that deal. They would get ownership of the account but they will be billed $140 Dollars a month (current rate of the T-Mobile ONE Plan). Any special promotions and/or pricing does not transfer over. So if you have 5 lines simple choice (grandfathered) unlimited Plan for $100 .... unfortunately that plan will not get transfered over to the new owner... they would have to get the T-Mobile ONE Plan for 5 lines.... i think its currently $160
Just making sure you are aware of the fine print of changing ownership of the lines.