Great — here are well-regarded eco‑friendly boutique hotels and small resorts across Sri Lanka, with a short note on what makes each sustainable so you can pick by region and vibe.

Top picks (shortlist — strong sustainability credentials)

• Jetwing Vil Uyana — Sigiriya (Cultural Triangle)

  • Why choose: Built around a restored/artificial wetland and designed with low‑impact, eco‑architectural principals; long-running programmes for energy/water/waste reduction and local community training. Excellent if you want wildlife, birding and an ecological design focus. (en.wikipedia.org)

• Ulagalla by Uga Escapes — Anuradhapura / Thirappane (Cultural Triangle)

  • Why choose: LEED/green‑building practices, large on‑site solar farm (generates a big share of its power), organic gardens, rainwater harvesting and community programmes (including elephant conservation efforts). Good for private‑villa style stays and conservation‑minded travellers. (ugaescapes.com)

• Santani Wellness Resort & Spa — near Kandy (Knuckles foothills)

  • Why choose: Purpose‑built wellness resort with “architecture of silence” focused on natural ventilation (reduces energy use), reclaimed/local materials, advanced water‑reuse and low‑impact construction. Strong wellness + sustainability combination. (Santani.com)

• Kalundewa Retreat — Dambulla / near Sigiriya

  • Why choose: Small, low‑density retreat on large grounds with organic gardens, substantial use of solar power, rainwater/irrigation systems and farm‑to‑table dining. Quiet, rural setting that emphasises conservation and local sourcing. (kalundewaretreat.com)

• Ravana Garden (Ravana Garden Sustainable Luxury Boutique Hotel) — Southern coast / Hambantota area

  • Why choose: Tiny boutique (few suites) with solar energy, rainwater recovery, organic garden and many single‑use plastics eliminated — focused on small‑scale sustainable luxury and Ayurvedic spa. Ideal for a low‑footprint beach/coast option. (ecobnb.com)

Other eco‑conscious boutique options (region + quick note)

• Abode Ahangama — South coast (Ahangama): small coastal boutique with locally made furnishings, community initiatives and emphasis on natural materials and beach‑clean activities. (bytheboutique.com)
• Flameback Eco Lodge — southeast (Weerawila / Yala area): built in harmony with its natural setting, wastewater treatment, recycling and organic gardens; good for nature/lagoon area stays. (hotel-boutique.it)
• Chena Huts (Uga Escapes) — near Yala National Park: low‑impact huts designed for wildlife viewing and conservation engagement (part of the Uga sustainability programme). (luxurytravelmag.com.au)
• The Plains Green (Nuwara Eliya region): boutique mountain property using recycled and reclaimed building materials and a farm‑to‑table approach. (theplainsgreen.com)

Practical tips for choosing & booking

• Decide region first: Cultural Triangle (Sigiriya/Anuradhapura) for Ulagalla, Vil Uyana, Kalundewa; Central Highlands (Kandy/Knuckles) for Santani; South Coast for Abode, Ravana Garden; Yala area for Chena Huts/Flameback. That saves travel time.
• Sustainability claims vary in type and proof: some properties have formal certifications (e.g., LEED at Ulagalla) while others publish their own sustainability policies — ask hotels for recent evidence (solar capacity, water treatment, waste‑reduction stats) if that matters. (ugaescapes.com)
• Small = limited rooms: boutique eco properties often have few rooms — book early in high season (Dec–Mar for south coast / Nov–Apr for east coast) if you need specific dates.
• Experiences matter: many of these stays include farm tours, herbal garden/ayurveda experiences, wildlife drives or community visits — check what’s included vs. extra cost.
• Transfers & access: several properties are remote (Santani, Ulagalla, Kalundewa) — factor in airport transfers or private car hire.

If you want, I can:

• Narrow this to 3–4 options in a specific region (south coast, Cultural Triangle, Kandy, or Yala), or
• Check current prices/availability for specific dates and return direct booking links (I’ll look up live availability).