LaTeX beamer: pagenumbering appendix

I have two templates I want to fit together.

The first part (Make desired footline) is to add the footline to the Berkeley-Theme while still be able to use the logo. This works like charm so far.

My problem however is the second part where I want to create the desired Roman Appendix numbering (as seen in the slides). With this code I found only my footline diapperes and only a white footline with the correct pagenumbering is present.

Is there a way to combine both such that I still have the footline but the numbering is the way I want it to.

Thank you in advance!

PS: Numbering should be as following:
For the normal slides: 1/x, 2/x, ..., x/x
For the Appendix: I, II, III, IV, ...

\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\setcounter{subsection}{1}

\usetheme{Berkeley}
\usecolortheme{seahorse}
\usefonttheme{serif}
\useinnertheme{rounded}

%%Make desired footline
\makeatletter
\setbeamertemplate{footline}
{
  \leavevmode%
  \hbox{%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,center]{author in head/foot}%
    \usebeamerfont{author in head/foot}\insertshortauthor~~\beamer@ifempty{\insertshortinstitute}{}{(\insertshortinstitute)}
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,center]{subtitle in head/foot}%
    \usebeamerfont{title in head/foot}\insertsubtitle
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,right]{date in head/foot}%
    \usebeamerfont{date in head/foot}\insertshortdate{}\hspace*{2em}
    \insertframenumber/\inserttotalframenumber\hspace*{2ex} 
  \end{beamercolorbox}}%
  \vskip0pt%
}
\makeatother


%%Make Roman Appendix numbering
\setbeamertemplate{footline}[page number]
\defbeamertemplate{footline}{page number appendix}
{%
  \hfill%
  \usebeamercolor[fg]{page number in head/foot}%
  \usebeamerfont{page number in head/foot}%
  \insertpagenumber\kern1em\vskip2pt%
}
\makeatletter
\g@addto@macro\appendix{%
  \setbeamertemplate{footline}[page number appendix]%
  \renewcommand*{\insertpagenumber}{%
    \Roman{framenumber}%
  }%
}
\makeatother

\usepackage{appendixnumberbeamer}

%%No Navigation template
\beamertemplatenavigationsymbolsempty

%%Title
\title{My beamer slides}
\author{Just another guy}
\institute[ABC]{My famous ABC institute}
\date{worldwide, \today}

%\logo{\includegraphics[width=1.5cm]{./logo}}

\begin{document}

\section{First Section}
\begin{frame}{First slide}
First slide (1/2)
\end{frame}

\begin{frame}{Second slide}
Second slide (2/2)
\end{frame}


\appendix

\section{Appendix}
\begin{frame}
First appednix (I)
\end{frame}

\end{document}