Hey TreeGlow. Happy housewarming! The really good news is that cleansing doesn't have to include sage or burning. There are a million ways to do it and you will get great suggestions here.
Essentially cleansing in my experience needs a few elements. There is the cleaning piece which removes any negativity, and then you go back in immediately and fill the space with good energy. In cleansing you empty a space and create a vacuum and you must fill that empty space with the good things of your choosing so that any negativity doesn't just rush back into the empty space created.
What you need to cleanse with: something that you feel will clear the space.
You could take water and consecrate it. Steep cleansing herbs like rose or sage...or whatever in it....make almost like a steeped sun tea with it.....the light of the sun will boost the herbs of your choosing and imbue them with cleansing powers. You can then put the filtered cleaning water into a spray bottle and go through the space.
You can use an aromatherapy oil diffuser.
You can cleanse with scent.
You can aspurge.
Literally, do what speaks to you.
Alternately, you can go through the space with a consecrated besom/broom and literally sweep out any negative energy. Or use a feather.....
A chant or Incantation you write can be said while you go through. Be specific about what is and is not allowed in the space and do not waver. Use their herbs that appeal to you for the work. Go online or look in a book...listen to your inner voice. This is your work and you are master of the space. You will know what to do. Have ideas about what you will do and what you will allow. Is there something peaceful there? It's an old building. What will you allow and not allow? What will you share?
To bring energy back into a space you can use a candle to light it up. Annoint the candle with warm loving correspondences. Bring it through the space again....this time feel the love and protection flooding into the space....
Heck, you can even bake a crumble or pie, or bread, and diffuse love into the air that way....
A few things to keep in mind. I open windows to allow for escape of energies. I do the initial cleansing going counter clockwise (widdershins) and start at a point that feels correct like a door or window. This helps get the energy out. I pay special attention to corners, Windows, doors, closets, bathrooms, drains and even power outlets and Internet connection portals. These are ways things come and go from spaces. Also any nooks and crannies energy can pool and stagnate.
When I fill the space I go clockwise (deosil) and pay attention to the same important points.
Does that help? If you have any more specific questions about the techniques I use you can always shoot me a pm.
Know you can do this.....people have special power when the space belongs to them. It is your plane and your space. Knowing and confidence in your ability to create a safe home space is crucial.