I only found a way to:
<TextBox Text="Text!"
IsReadOnly="True"
IsTabStop="False"
BorderThickness="0"
>
<TextBox.Style>
<Style TargetType="{x:Type TextBox}">
<Style.Triggers>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsMouseOver" Value="False" />
<Condition Property="IsFocused" Value="False" />
</MultiTrigger.Conditions>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<TextBlock Text="{TemplateBinding Text}" />
</ControlTemplate>
</Setter.Value>
</Setter>
</MultiTrigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
There is another option not so big?