I know it might sound a bit "woo", but if you want to put your mind at rest, maybe get a white sage smudge stick (lots of online places sell it) , light it, and gently walk round the room, saying a prayer (The Lord's Prayer is as good as any) or a blessing or just asking that any spirits in the room who need to move on can do so. Make sure you put the smudge stick somewhere safe to burn out.
If you'd rather not use a smudge stick, then ordinary incense or even a nice white candle (again, tealight is fine) in a safe fireproof holder, walking round the room with it. If you want to go the whole way, as it were, then you can use the four elements (air - incense; fire - candle; water - plain boiled water will do; earth - a little bit of rock or sea salt, just a few grains in each corner). There are lots of very nice, safe cleansing rituals online, and I know it might sound daft, but every time I've ever moved house, just for my own peace of mind, I've used them, and often regularly throughout the year too. Again, it might sound a bit "woo", but energy builds up in a place just as dirt does, so a good clean now and then won't do any harm (including opening the windows or doors and "brushing things out" with a broom or brush).
Whether you belief in them or not, from a psychological point of view they can be very settling.
Or if you're really worried, have a word with the local church and ask what help they can give you. But honestly, someone has been a good, kind person in life, they're not going to stop being that good, kind person when they move on, if you believe in an afterlife. (We have our own ghost, Zelda, who used to live here and really does get very cross when we move the plantpot. I am not making this up. And a lot of my friends are nurses or ex-nurses, and pretty much all of them have seen spirits in hospital. And they're all the most down-to-earth, no-nonsense people you could hope to meet.)