# How to selectively substitute a letter with another symbol representing the same letter

First of all, sorry for the vague title, feel free to edit if you have a better one.

I have two mathematical entities represented by the same symbol, say the letter a, that should be used only in math-mode. As both entities are usually represented with a, I would like to keep the same letter for both of them, but making them appear a little different.

How would you achieve that?

1. Finding an alternative symbol (preferred way; I tried using \mathcal but it supports only capital letters---otherwise the result would be satisfactory)
2. Loading another font altogether and print one of them in the second font
3. Another option

Requirements:

1. Support for both math-mode and bold face
2. No superscripts, hats, tildes etc.

Here is what both symbols should be able to do:

\documentclass[border=5pt]{standalone}
\usepackage{mathtools}
\begin{document}
$a$ $\boldsymbol{a}$ $\hat{\boldsymbol{a}}$
\end{document}


You could use \mathsf. But are you sure this is a good idea? I think it could be very hard for the reader to distinguish the two.
\documentclass[border=5pt]{standalone}
$\symbola\symbolb% \boldsymbol{\symbola}\boldsymbol{\symbolb}% \hat{\symbola}\hat{\symbolb}% \hat{\boldsymbol\symbola}\hat{\boldsymbol\symbolb}$