If I am reading this correctly, you want the space between the paragraphs not the lines, right?
If so, then you need to increase the spacing after. You can do this with styles in Word, but you have to select the format drop down and paragraph to get to that granular level. Just double your point size and you'll get double spacing after paragraphs.
If you want double spacing between each line in the paragraph, then you need to use line spacing at exactly and use a point size that is double the size of the point size you have listed.
I haven't used D2D, so I can't say whether you can customize styles through them or if you have to bring in custom styles, but I find that using ems for the CSS works best. If you can build a basic CSS, all you need to do is worry about putting in the styles.
Here's some basic styles I built for a CSS. The Body is the default. fm-para is a basic paragraph no changes, fm-paralast is with spacing between paragraphs, fm-paradouble is with double spacing between each line.
body {
font-size: 1em;
line-height: 1.1;
margin: 0 2% 0 2%;
padding: 0;
border: 0;
outline: 0;
font-family: Bookerly, Georgia, Palatino, Baskerville, "Times New Roman", serif;
}
.fm-para {
font-weight : normal;
font-style : normal;
font-size : 1em;
line-height : inherit;
margin-top : 0em;
text-align : left;
margin-bottom : 0.2em;
}
.fm-paralast {
font-weight : normal;
font-style : normal;
font-size : 1em;
line-height : inherit;
text-align : left;
margin-bottom : 1em;
margin-top : 0em;
}
.fm-paradouble {
font-weight : normal;
font-style : normal;
font-size : 1em;
line-height : 2em;
text-align : left;
margin-bottom : 1em;
margin-top : 0em;
}