Inverse of binary entropy function for $0 \le x \le \frac{1}{2}$

I'm trying to find the inverse of $H_2(x) = -x \log_2 x - (1-x) \log_2 (1-x)$^[1] subject to $0 \le x \le \frac{1}{2}$. This is for a computation, so an approximation is good enough.

My approach was to take the Taylor series at $x=\frac{1}{4}$, cut it off as a quadratic, then find the inverse of that. That yields

$$H_2^{-1}(x) \approx -\frac{1}{16} \, \sqrt{-96 \, x \log\left(2\right) + 9 \, \log\left(3\right)^{2} - 72 \, \log\left(3\right) + 96 \, \log\left(4\right)} + \frac{3}{16} \, \log\left(3\right) + \frac{1}{4}$$

Unfortunately, that's a pretty bad approximation and it's complex at $H_2^{-1}(1)$. What other approaches can I take?

^{[1] I originally forgot to write the base 2 subscript (I added that in a later edit)}

A rather coarse approximation of $H_2(x)$ on the said interval is $4 \log(2) x(1-x)$. Hence a crude approximation for the inverse is: $$ H_2^{-1}(y) \approx \frac{1}{2} \left(1- \sqrt{1-\frac{y}{\log(2)}}\right) = \frac12\frac{y}{\log(2) + \sqrt{\log(2)\left(\log(2)-y\right)}} $$ This initial approximation should be refined with Newton-Raphson method.

A nice approximation I found in this thesis:

$ \frac{x}{2 \log_2 (6/x)} \leq H_2^{-1}(x) \leq \frac{x}{ \log_2 (1/x)}$