@CaliaMoko Hi Vicki
You are in luck - the consensus is that a hard, reflective, floor is a good thing (ideally coupled with treated walls)
This will give you a good compromise of the room sounding “live” (for both recording and mixing) but still controllable with treated walls
So with the floor if it is solid concrete you could consider just leaving it exposed and brighten it up with some paint/rugs
Alternatively any hard covering would be good such as wood, laminate or vinyl
Then, depending on the dimensions of the room, you should consider some acoustic treatment on walls - ranging from hanging some heavy curtains to proper acoustic panels and bass traps
I think it is best to get everything set up first and “live with the room” for a while so that you settle upon a comfortable setup - eg where will you record vocals, where will you sit when mixing etc. - try out different areas of the room as moving just a small amount could drastically affect the sound
Once settled you can look in to options for the wall (and possibly ceiling)