Great — here are six of Sri Lanka’s top eco-friendly resorts for a relaxing vacation, with why each stands out and what kind of trip it’s best for.

1. Jetwing Vil Uyana (near Sigiriya) — classic eco‑luxury in a restored wetland

• Why: Built around a man‑made wetland and forest, strong habitat restoration and wildlife programmes (loris conservation, birdlife), locally sourced food and low‑impact construction.
• Best for: Nature lovers who want wildlife viewing from your villa (birding, night walks) plus quiet luxury. (jetwinghotels.com)

2. Santani (near Kandy) — wellness + low‑impact design in the hill country

• Why: Wellness retreat with architecture that uses natural ventilation and site‑sensitive materials, extensive organic gardens and a strong Ayurvedic/wellness focus that reduces energy use and promotes slow living.
• Best for: Restorative stays (Ayurveda, yoga, spa) away from heat and crowds. (wallpaper.com)

3. Ulagalla by Uga Escapes (Anuradhapura area) — boutique eco‑villa estate

• Why: Early adopter of green certifications for boutique hotels in Sri Lanka (LEED mentioned for the Uga group), on‑site organic farming, solar and biogas use, water treatment and community engagement.
• Best for: Private‑villa relaxation, cultural excursions and farm‑to‑table dining. (ugaescapes.com)

4. Chena Huts by Uga Escapes (near Yala) — low‑profile safari lodge with sustainability focus

• Why: Built to blend into the landscape, uses solar power and energy‑efficient systems, organic garden/seaweed composting and Travelife/eco‑certified operations and local hiring.
• Best for: Relaxing safari base with easy access to Yala National Park (wildlife + quiet pools/spa). (srilankawildroom.com)

5. Anantara Peace Haven Tangalle (Tangalle coast) — coastal resort with conservation projects

• Why: Active turtle‑conservation partnership (IUCN/DWC), mangrove restoration, rainwater harvesting, eliminated many single‑use plastics and runs local farm/paddy projects.
• Best for: Beachside relaxation with meaningful conservation experiences (turtle watching, mangrove walks). (Anantara.com)

6. Cape Weligama (South coast, Weligama) — design‑forward resort with community & marine initiatives

• Why: (Resort operates a number of sustainability/community programmes including local sourcing and marine awareness; see major travel profiles and the resort’s stated initiatives.)
• Best for: Luxe coastal stays with panoramic views, day trips to local surf/beach towns and community‑based experiences. (cntraveler.com)

Quick tips for choosing and booking

• Decide the vibe: choose hill country (Santani) for cool wellness; inland/wetland (Vil Uyana, Ulagalla) for birds and quiet; south coast (Anantara, Cape, Chena Huts) for beaches + safaris.
• Peak vs low season: December–March (dry south/wildlife) and April–September (drier in the cultural triangle) are busy — book well ahead if you want a specific villa.
• Ask before you book: if sustainability credentials matter to you, request specifics (waste/water/energy stats, local community projects, certifications) — many properties publish recent sustainability pages or reports.
• Combine stays: a relaxing 10–12 day trip can pair a hill/wellness stay with a coastal/safari stay without long internal flights.

If you’d like, I can narrow this to resorts within a specific region (south coast vs central hills), pick options for a particular travel date range, or check current room availability and rates for any of these — tell me which resort(s) you prefer.