If your using K-cups you do not need a filter. But if you found a coffee you really like, as I did, than I highly recommend the Ekobrew container. It allows you to make your coffee as strong or as weak as you want because you decide how much coffee to use each time. They are easy to clean and refill and they reduce the amount of waste.
Hello Doris! For the Keurig B145 OfficePRO, I purchased the Solofill refillable filter located on Amazon at Solofill Cup, Refillable Cup For Keurig Single serve cups Brewers, Black . This filter is a perfect fit for the Keurig B145. You have to be very careful to purchase the correct size refillable filter for your brewer. If your refillable filter is the wrong size and you force your brewer to close anyway, you can damage the brewer.
The Solofill filter seems to be well made, the lid snaps closed well. It's also really nice that this refillable filter is an all-in-one - the holder and filter mesh are all built in together. It does not require disposable paper filters, too, like some of the other refillable holders on the market. I really like this reusable filter but I will say that I have not yet attained the perfect grind for the filter. The first batch of coffee I ground to use in the filter comes out too weak for me, even when I fill the filter full, so I'm going to try a finer grind and/or darker roast next time. Good luck!