There is no band that you can call similar to Pink Floyd. David Gilmour had a unique tone on his guitar work, and what came out of Roger Waters' head when he wrote is uniquely Waters.
The closest you can try to come is to listen to some other progressive rock bands of the late '60s - mid '70s era that don't have a uniquely-identifying musical style. I'm not saying not to investigate these bands, in fact, I think you should. It's just that one particular instrument or the lead singer will instantly tell you it's not Floyd"
Emerson, Lake & Palmer
Focus (Dutch band)
Led Zeppelin (was not prog rock per se but did venture into that genre with later albums, still, they are nothing like Floyd)
I would give a listen to:
The Soft Machine
Earlier King Crimson
The Moody Blues