Many have started with Hennessy. If you go that route - I think the REI sales are over - and buy from them, you used to be able to opt for their Hex Tarp by paying the retail difference between it and the standard, smaller, tarp that comes with the hammock. I think you'd like the utility of the large Hex.
But give us an idea of your size (length, weight). For example, if you are in the 6 ft + range or the 250lb + range, there is probably a better fit for you than the Hennessy.
Many hammock campers end up with more than one hammock because 1) after some experience they have a better idea of what they are looking for. 2) Many hammocks cost under $100, with "On Sale" bargains for $50, so they aren't costly. 3) After you've finally found "your precious" the hammock you had before can become a loaner for friends.
That the "flatter lay" comes from the suspension rigging. You don't pull it tight. You hang with about a 30° (or 60° depending on which end you measure from) angle. That puts sag in the hammock so the ends are a distance apart that's about 83% of the hammock length. So if the hammock were 10 ft long, you'd hang it so the hammock ends are about 8 ft apart. The lines from the hammock ends are connected to the trees so the bottom of the hammock is about chair height (18") from the ground - so getting in/out is like getting out of a chair.
That sag allows you to lie in the hammock at an angle to the center line of the hammock. It's that angle, head right, feet left (or vice versa) that gives you the flat lie.
Those numbers are not golden - they are "-ish's", "sorta's", and "about's".
The basic setup is a hammock with a built-in, or separate, bug net, tarp, top quilt, and under-quilt. If you have a sleeping bag, you can use that instead of a top quit (just unzip it most of the way but keep the foot box). If you can a camp sleeping pad, you can put that in the hammock instead of the more comfortable under-quilt.
The pad or under-quilt is needed because, in a hammock, your heat loss is from air currents passing under it.