Both arrive to Paris (you from BLR, your wife from LHR); check into a centrally located romantic hotel (Saint-Germain or near the Seine) to drop bags and freshen up.
Leisurely stroll to see Notre-Dame exterior, Pont Neuf and riverside bookstalls; gentle, romantic first afternoon in Paris (most outdoor sights open 24/7, check Notre-Dame access).
A quintessential romantic introduction to Paris — 1-hour light commentary cruise past illuminated landmarks; book a sunset or early-evening sailing (typically 10:00–22:30 operating hours).
Choose between a dinner cruise for intimate views or a cozy riverside restaurant with classic French cuisine and Champagne — reserve in advance for the best window seat.
Dine with a view — book early for an Eiffel Tower restaurant or a fine-dining romantic spot for sunset and glittering city lights; Eiffel restaurants typically open evenings until late (reserve ahead).
Quick breakfast and board the train toward Kleine Scheidegg for the Jungfraujoch 'Top of Europe' excursion; mountain trains start early (check seasonal timetables).
Ascend by cogwheel train to Jungfraujoch for snowy panoramas, ice palace and mountain terraces; summit facilities typically open from ~08:00–16:00 (weather-dependent).
A longer scenic rail journey through central Switzerland and the Gotthard route into the Italian-speaking canton of Ticino; settle in for alpine-to-mediterranean scenery.
Take a romantic 1-hour ferry/boat ride to enjoy the shoreline villas and small islands; check local schedules (most run through evening in high season).
Breakfast, check-out and travel south to Como/Bellagio — combination of train and ferry takes ~1.5–2.5h depending on route (Lugano → Como S. Giovanni or via Chiasso).