Installing Additional Stairs for Duplex

My family and I live on the first 2 floors oa a 3 fam house. We have a tenant on Floor 3. There is currently only a single staircase leading from the first floor to the top – lefthand side of the house – pretty standard. We’ve been using this common staircase as we go from Floor 1 (kitchen, L/R, access to our yard, etc.) to Floor 2 (bedrooms). It’s not that bad…but we’d really like to be “self-contained” We are very interested in installing a small spiral or similar-type of staircase connecting floors 1 & 2 so that we really have a contained duplex. We think that connecting the small middle rooms to one another.

Has anyone done this before? I know that there are those that say not to… But, I’ve seen some photos and examples and we like it. So, has anyone used a person/company they like? Ball park price? Did you have the stairs custom made, or did you buy the stairs? Someone recently posted a link to the Arkestairs company and they really looked interesting.

Thoughts please!