Anta, you are getting a lot of confusing information. If your Rolleiflex has a Xenar lens, then it uses filters that are Rollei Bayonet I (also known as Bay 1 or R1) size.
1. The easiest way to use filters is to buy the Bay I Rollei, Yashica, or third party filters. Then the Bay I hood will fit over the filters when it clips on the external bayonet mount.
2. Because many TLR cameras used Bay I, the filters are readily available (at least in USA). Companies like Tiffen made Bay I filters.
3. If you want to use other size filters, you need a Bay I - size xxx adapter.
4. An inexpensive option for filters is to use Series V or Series VI filters. Few people use them now, so they are cheap. You would need a Bay I - Series V or VI adapter.
5. If you want to use a polarizer, you can use a normal linear polarizer. You do not need a CPL or circular polarizer. Rollei and other companies made Bay I polarizers, but they are hard to find and, because of age, many have delamination problems.
Have fun. The Rolleiflex is a great camera.