5G Signal Booster

No they don't. There are boosters available but they are 4G LTE boosters. If you can get 2 bars of 5G you might be able to get 3 and a cleaner signal with an external antenna. There are 2X2 MIMO and 4X4 MIMO external antennas. Waveform.com has the complete package and support that backs up what they sell. The external antenna is a better solution, in my opinion, as a good booster is more expensive and an external antenna is still needed, and well they are 4G LTE boosters currently. I installed a weBoost for my sister which was ~$600 and that was 4G LTE. It works but her location is still a real challenge so she needs an additional 20' of vertical reach to really get the signal.

You can, and I recommend, checking out Nater Tater YouTube videos on the T-Mobile gateways and antennas. He has done videos on all three. There are guides that Waveform has made that cover doing the connections. It does take a little tech know how as you have to open the gateway to attach the connections. The connectors are very tiny and delicate so you have to exercise extreme care when detaching the internal antenna lead and attaching the dongles for the external connections. It can be done if care is taken and patience is used. Waveform engineers can and will offer suggestions for antenna mounting. On top of the house is NOT always the best location. You have to consider using the home possibly to shield the signal from noise so it takes a little experimentation. The side benefit of the external antenna is that the location of the gateway within the home is easier to improve for coverage with local WIFI. 

If you are receiving the n71 a 2X2 MIMO would work but for a n41 signal you would want the 4X4 MIMO. My take is if T-Mobile upgrades the n71 to an n41 the best choice is to have the 4x4 MIMO antenna just in case they do so. They did upgrade ours here about 14 months after the initial deployment of the n71 so that is a factor to consider. The external antenna can help a great deal.

So, an inexpensive booster with an internal antenna will not do what you want. Just my take. It is sort of like a free piano. Just as I was told the free piano turns out to be the most expensive one in the end. We dodged the free piano once we got the estimate to make it useful.

I live in between T-mobil towers and get very weak signal

 T-mobil did provide a 4g booster that works well, but i had to push for it.

I'd recommend looking more towards an external antenna myself.  T-Mobile does have devices with external antenna, and they're better at filtering/picking up a weak signal (in a certain direction), while a booster just amplifies all … including noise, and typically isn't directional.  Most companies are not in the business of 'boosting/amplifying' signal anymore, as they are not requiring carrier approval.

Como @iTinkeralot states - NaterTater has info, and has tested antenna for T-Mobile home internet devices.  The latest device also has ports for connetion.