Alas, yet another question on font selection in mathematics.
I want to avoid bold extended and use bold instead. My main font is computer modern. For text, I managed to change the appearance of bold with the help of this question. Also, changing the font for \mathbf wasn't to hard. But how can I make \bm or \boldmath match the rest of the fonts?
M(n)WE:
\documentclass{scrartcl}
\usepackage{bm}
% Bold in text.
\renewcommand{\bfdefault}{b}
% Bold in \mathbf
\DeclareMathAlphabet{\mathbf}{OT1}{lmr}{b}{n}
\DeclareMathAlphabet{\mathbfit}{OT1}{lmr}{b}{it}
\DeclareMathAlphabet{\mathbxit}{OT1}{lmr}{bx}{it}
\begin{document}
\begin{itemize}
\item Text:
\textbf{bold BOLD}
\item \texttt{mathbf}:
$\mathbf{bold BOLD}$
\item \texttt{mathbfit}:
$\mathbfit{bold BOLD}$
\item \texttt{mathbxit}:
$\mathbxit{bold BOLD}$
\item \texttt{bm}:
$\bm{bold BOLD}$
\item \texttt{boldmath}:
{\boldmath $bold BOLD$.}
\end{itemize}
\end{document}
The issue is that the last two examples show much wider characters than the other examples. In fact, even wider than in the \mathbxit-example.
How can I get the same bold-non-extended letters in \boldmath? Plus: is there a non-extend bold version of \mathcal-letters?

\bmoutside math mode is not raising an error is an oversight, it is not intended to do work in that context. – David Carlisle Feb 10 '20 at 10:44\mathrmthe math italic letters are by default\SetSymbolFont{letters} {bold}{OML}{cmm} {b}{it}so already using b not bx – David Carlisle Feb 10 '20 at 10:49bm-example is wider than the "O" in the\mathbxit-example (at least, it seems), and both are much wider than themathbfit-O. – Bubaya Feb 10 '20 at 11:28\DeclareFontShape{OML}{lmm}{b}{it}{%with a substritution\DeclareFontShape{OML}{lmm}{bx}{it}% {<->ssub*lmm/b/it}{}so b and bx are the same thig – David Carlisle Feb 10 '20 at 11:37omllmm.fdcorrectly if I read it as there is onlynandbx, andbis only a synonym forbx, but there is no lighter version of boldness? – Bubaya Feb 10 '20 at 11:51