custom page except front and index

I want to format my document so as to fit its contents as I would like, but not keep this format for the front page and the index; as I need large margins for notes & equations but this particular layout make the cover and index look very weird, everything being put on the side.

I use this code to custom its format:

setlength{oddsidemargin}{0cm} 
setlength{evensidemargin}{0cm}    
setlength{marginparwidth}{5cm}    
setlength{textwidth}{13cm}
setlength{textheight}{23cm}

and want to know if it is possible to either:

• reset it locally while being true on global
• set it on locally while being off on global

If this problem has no solution in LaTeX, I will simply save two documents, one unformatted and one formated and use pdf to merge the front page and index of the unformatted and the content of the formated.

documentclass[oneside]{book}
usepackage{lipsum}
usepackage{geometry}
  geometry{margin=3cm}

usepackage{makeidx}
makeindex

begin{document}

begin{titlepage}
textbf{Titlepage}\
lipsum[1-4]
end{titlepage} 
    
tableofcontents

newgeometry{margin=0.5cm}

chapter{Small marginsindex{Small Margins}}lipsum

restoregeometry

chapter{Default marginsindex{Default Margins}}lipsum

newgeometry{margin=6cm}

chapter{Large marginsindex{Large Margins}}lipsum

restoregeometry    

printindex 
    
end{document}