bbell- If you go with Rockauto, the # you SHOULD need is Denso 2349009- same as original Toyota/Lexus 89467-41011. If you take a mirror (if your lucky, the # is facing up, if not, you'll need a mirror), the # is laser etched on the barrel of the sensor and isn't real easy to read but with a flashlight and good eyes you CAN see it. The front and rear sensors are the same so you can double check the # on the front sensor but the sensor you probably need is the rear. They are mounted in the exhaust mainifolds, front and rear. The one in the cat. conv. outlet is different. The code that you read with the obdII scanner will tell you whether it is front or rear. I believe you are much better off using original eq. Denso sensors- from whatever source you choose to get them. B2S1 will be front (easy one) and B1S1 will be the rear exhaust manifold. Good Luck!
before you start make sure you spray some PB or WD40 on them to help break up the rust and if you can find the o2 sensor tool that looks like the close end of wrench use that instead of the socket one with the slit down the side.