It all depends on what you want to spend and what you want the freeview box (STB) to do. Do you want to just "convert" the TV to Freeview or take advantage of Freeview Plus and be able to record and or view another channel at the same time.
I live in Devon and our analogue signal was one of the first to be turned off!! I Have a non HD BV5 and use a Humax PVR 9200T with a twin tuner and 320GB hard drive. This model was in the STB controller list on the TV so works with my Beo4 & Beo5. It allows me to watch one program and record another or record two and watch a third depending on wich channel they are.
I chose Humax as they have an excellent record for updating the software even on the older models, they seem reliable and are very easy to instal and use. I bought mine here.
You can go for a simple cheap single tuner Freeview STB and they go anything from about £20 up.
Or go for twin tuner + hard drive recorder from under £100
Some DVD player/recorders have Freeview tuners built in.
I had a look at the user manual for the BV3 on here and it seems it has an STB controller option. Does yours have that? If it does and you choose a model in the list you will get Beo4 compatibility, otherwise if it's not in the list you'll be using 2 remotes.
Others will have their favourite model and no doubt will let you know.
Good luck
Stoobie