Internal floor splitting double height entrance

[Phyllis70]

Hi All

1st time poster from an average reluctant DIYer. Can do certain jobs whilst badgered by missus but this one involves structural so way beyond my limited skills

Ive really just after a ballpark idea of what might be involved and guesstimates on costs to build an open plan snug with access from our existing half landing, so Missus can make use of the space above our entrance

Saves me stressing over painting the ridiculously high ceiling as well!

Its a fairly new build house, by Avant, only 4 years old. Walls to left and right are timber i believe

We would like to keep the balustrade in some form or another, for light.

Any and all help / comments appreciated

Cheers in advance

Dave

[ProDave]

In principle you should be able to find the structural points of the wall at first floor height (that will probably be supporting the other floors) and span a floor from those.  but to access your new mezanine floor you will need a short staircase up from the half landing but there I see a problem, those stairs will be cutting across a dooorway.  Picture from below may help?

[Mr Punter]

Would you please straighten up the picture of the stag?