How tall will the new viv be ?
How far will the basking spot be from the tube ?
Will you be mounting under the lid ( excellent ) or on ontop a mesh lid ( not good ).
T5HO or T8 ?
In a reflector hood , or just a bare tube ?
See this for how to set up for a good beardie tank :
viewtopic.php?f=34&t=235611
I'd recommend a T5HO in a reflector hood , rated at least 10%UVB for a tank 18" tall , taller you will need a T5HO rated 14%UVB in a reflector hood ( only Arcadia Reptile have good quality T8 and T5ho tubes rated 12%UVB and 14%UVB.
If you are buying a new fixture (reflector hood) consider buying an Arcadia Slimline Kit (they come with an Arcadia tube (your choice) in the kit ready to be turned on.