REVISED APPROACH
\itfrac
shown in \displaystyle
, \textstyle
, \scriptstyle
, and \scriptscriptstyle
.
\documentclass{report}
\usepackage[sloped]{fourier}
\DeclareSymbolFont{mathit}{T1}{fut\mathfamilyextension}{m}{it}
\DeclareMathSymbol{0}{\mathalpha}{mathit}{`0}
\DeclareMathSymbol{1}{\mathalpha}{mathit}{`1}
\DeclareMathSymbol{2}{\mathalpha}{mathit}{`2}
\DeclareMathSymbol{4}{\mathalpha}{mathit}{`4}
\DeclareMathSymbol{5}{\mathalpha}{mathit}{`5}
\usepackage{scalerel}
\newcommand\itfrac[2]{\mathchoice
{{\textstyle\frac{\,\displaystyle#1}{\!\!\displaystyle#2}}}
{{\frac{\,\scriptstyle#1}{\!\!\scriptstyle#2}}}
{{\frac{\,\scriptscriptstyle#1}{\!\!\scriptscriptstyle#2}}}
{{\frac{\,\scriptscriptstyle#1}{\!\!\scriptscriptstyle#2}}}
}
\begin{document}
\centering
\[
1\itfrac{1}{1} + \itfrac{12}{24} = \itfrac{250}{100}
\]
\[\textstyle
1\itfrac{1}{1} + \itfrac{12}{24} = \itfrac{250}{100}
\]
\[\scriptstyle
1\itfrac{1}{1} + \itfrac{12}{24} = \itfrac{250}{100}
\]
\[\scriptscriptstyle
1\itfrac{1}{1} + \itfrac{12}{24} = \itfrac{250}{100}
\]
\end{document}

It is possible the \itfrac
macro can be simplified as
\newcommand\itfrac[2]{\mathchoice
{{\textstyle\frac{\,\displaystyle#1}{\!\!\displaystyle#2}}}
{\frac{\,#1}{\!\!#2}}
{\frac{\,#1}{\!\!#2}}
{\frac{\,#1}{\!\!#2}}
}
It works the same in this MWE, but I am not 100% sure whether that would be the case for all use cases.
ORIGINAL APPROACH
To elaborate on a comment made (though not really an answer, per se, this is what I was indicating..., calling it \itfrac
.
\documentclass{report}
\usepackage[sloped]{fourier}
\DeclareSymbolFont{mathit}{T1}{fut\mathfamilyextension}{m}{it}
\DeclareMathSymbol{0}{\mathalpha}{mathit}{`0}
\DeclareMathSymbol{1}{\mathalpha}{mathit}{`1}
\DeclareMathSymbol{2}{\mathalpha}{mathit}{`2}
\DeclareMathSymbol{4}{\mathalpha}{mathit}{`4}
\DeclareMathSymbol{5}{\mathalpha}{mathit}{`5}
\newcommand\itfrac[2]{\textstyle\frac{\,#1}{\!\!#2}}
\begin{document}
\begin{equation}
1\itfrac{1}{1} + \itfrac{12}{24} = \itfrac{250}{100}
\end{equation}
\end{document}

1\textstyle\frac{\,1}{\!\!1}
into some kind of macro.