High-Res Casual Face Swap

I have a high-resolution family photo that i like but my son is not smiling. I have a separate photo where he is smiling. I simply need a clean, natural-looking swap—skin tones matched, lighting consistent, no obvious retouching artifacts—while preserving the full original resolution.

Deliverables:
• One seamless composite image returned in the same resolution and file format as the original.
• A flattened version plus, if you work in Photoshop, a layered PSD so I can make minor tweaks later.

Please work non-destructively and keep all facial details sharp. Quick turnaround appreciated; the job is straightforward for anyone comfortable with Photoshop, GIMP, or similar tools.