Handrail for Spiral Staircase (Surface Mounted vs. Side Mounted)

Hello everyone,
for our small spiral staircase, we would like to build a railing/fall protection. Now it is the case that a surface-mounted installation of a railing is probably quite difficult, since under our floor covering there is about 8cm of screed and 8cm of insulation. I think mounting the posts in the screed is certainly not stable enough.
So I see 2 possibilities: anchoring the posts in the underlying concrete (18cm reinforced concrete) (surface-mounted installation - but this would certainly require at least 20cm long screws and anchors), or a side-mounted installation of the railing.

What do you think about this? Is a surface-mounted installation with special screws and anchors even possible? The advantage would be that there is a suitable railing for the spiral staircase (Dolle). With a side-mounted installation, there is no exactly matching railing, and it will probably also be somewhat lower.

I look forward to your input. Thank you very much! :)
I have attached a picture of the staircase during the construction phase.

For a side installation, there is no exactly fitting railing,

Then go to a locksmith and have one made for little money. That's how I would do it at least.

Is this supposed to be a DIY project? If it is securely attached to the wall, smaller screws are also sufficient.