Latex font in scrbook class and bad printed result - pdf

Question

I have written a book using latex class scrbook and have found that the printed text in the proofs is not very easy to read, characters are thin and somewhat small. I would like advice on a more readable font that I could use.
Here goes my latex preamble:
\documentclass[
a5paper,
pagesize,
10pt,
bibliography=totoc,% <-- changed
numbers=noenddot, % <-- changed
headings=normal, % <-- changed
%DIV=9,
twoside=false,
%parskip=half,
]{scrbook}
In a previous work I have used the memoir class, with better results in the printed work:
\documentclass[9pt,openany]{memoir}
\usepackage[osf]{mathpazo}
\usepackage[mathcal,mathbf]{euler}
\usepackage{amsmath,amssymb,amsthm}
\usepackage[utf8]{inputenc}
\usepackage{graphicx,sidecap,tikz}
\usepackage[portuguese]{babel}
\usepackage{csquotes}
\usepackage{url}
\usepackage{siunitx} % automatic number formatting, decimal point alignment
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[backend=biber,style=authoryear,natbib=true]{biblatex}
\addbibresource{sample.bib}