Catalytic converter replacement

I have to replace one of my cats so would like to know if their were some that would improve the performance of my 2005 Tacoma. Do you need to replace the manifold as one unit? Thanks for any advice. I only have 250k miles on it so planing on having it another 10 years.

 

You do not have to replace the manifold itself

 

I’ve just ordered mine, replacing both front cats…and yes, they are one part with the manifold. Unless you buy a weld-on and cut it in.