What else will be in the room? A TV? If so where? Also what dies that fireplace look like? Can you share pics of the actual room please?

A question and a thought. Is the red lines shown to indicate a step making the area recessed? And how tall are the ceilings? If you have the same ceiling height I'd consider raising the flooring level. The electric fireplace can be easily remounted. I'd like the width for a sectional. Otherwise the sectional goes with the long section right up against the step.

My thought is the den could be used for tv watching.

Red line just shows the actual usable space

This is the space. There’s an electric wall mounted fireplace underneath the TV.

No steps between the space

Ceilings are 10ft tall

I would probably do a sofa and two chairs, nice comfy ottoman as table. Make sure your fireplace is wider than your tv. nice rug too

When configuring a family room, start by defining zones, seating/lounge, media/TV, and circulation, then orient furniture so the flow between them feels natural. Use area rugs or furniture groupings to anchor zones, and avoid pushing every piece against the walls: a more relaxed layout with some breathing space makes the room feel more inviting. Consider built-ins or cabinetry along one wall to handle storage (for books, games, media) and conceal clutter, which helps maintain visual calm.

Lighting (natural + layered artificial) should be part of the layout, e.g. reading nook near a window, ambient light for evenings, accent lamps for cozy corners. A thoughtful layout plus layered furnishings ensures the family room works for lounging, entertainment and everyday living without feeling chaotic.

With 4K tvs the current minimum viewing distance on an 85" is about 6 feet. Lower wall mounting than above a normal fireplace is optimum. An electric unit can be a lower horizontal configuration. A bunch of different spacings can work.

Consider 2 floor outlet locations for 120v receptacles.