\usepackage{dcolumn}
%here we're setting up a version of the math fonts with normal x-width
\DeclareMathVersion{nxbold} 
\SetSymbolFont{operators}{nxbold}{OT1}{cmr} {b}{n}
\SetSymbolFont{letters}  {nxbold}{OML}{cmm} {b}{it}
\SetSymbolFont{symbols}  {nxbold}{OMS}{cmsy}{b}{n}

\begin{document}
\makeatletter
\newcolumntype{d}{D{.}{.}{-1} } %decimal column as before
%wide bold decimal column
\newcolumntype{B}[3]{>{\boldmath\DC@{#1}{#2}{#3} }c<{\DC@end} } 
%normal width bold decimal column
\newcolumntype{Z}[3]{>{\mathversion{nxbold}\DC@{#1}{#2}{#3} }c<{\DC@end} } 
\makeatother
\begin{tabular}{l l d}
    Type &M & \multicolumn{1}{c}{N} \\
    Normal & 1 & 22222.222 \\
    Bold (standard)&10 & \multicolumn{1}{B{.}{.}{-1} }{22222.222}\\
    Bold (nxbold)&100 & \multicolumn{1}{Z{.}{.}{-1} }{22222.222}\\
\end{tabular}
\end{document}