You can use your regular BBT to temp vaginally, you don't need a specialized one.

The only thing that I will tell you is to wait to start vaginal temping when you begin a new cycle as your temp will be higher when taken vaginally and it will be hard to determine your O date.
Also too, you only have to insert the tip into your vagina. There was someone who mentioned putting it way up inside and that's not necessary.

Good luck! Let us know how you like vaginal temping! I'm changing to it if this cycle ever ends.