Here are Colombo properties that explicitly offer laundry and are set up for longer stays (serviced apartments / extended-stay suites). I pulled each entry from hotel/booking pages so you can check current rates and monthly options:

• Cinnamon Life — serviced apartments / extended-stay units (kitchen, internet, laundry services). (Advice.lk)
• Supun Arcade Residency (serviced-apartment style) — in-room washing machines, daily housekeeping and laundry service; suitable for longer stays. (cityzenbooking.com)
• Platinum One Suites / various serviced-suite properties in central Colombo — list of amenities includes laundry/dry cleaning, kitchenettes and long-stay options. (booking/property page). (chiangdao.com)
• Multiple serviced-apartment listings on Expedia / booking sites for Colombo (Horton Residence, Alexandra Apartment, Monaara Leisure, Lotus View, etc.) show “on-site laundry” and are marketed for extended stays. Use booking sites to compare monthly/long-stay rates. (Expedia.co.in)

Notes and next steps

• “Extended stay” in Colombo is commonly handled by serviced apartments (kitchenette/full kitchen + laundry) rather than traditional short-stay hotels. Major hotel groups (Cinnamon, Shangri‑La, Mövenpick, Taj) sometimes offer apartment/long-stay options — check each brand’s serviced-apartments page for the latest offerings and monthly rates. (Advice.lk)
• If you want, I can:
  • Look up specific monthly rates and availability for dates you have in mind; or
  • Produce a short list of 6–8 recommended options (with addresses, phone numbers and links) tailored to your preferred neighbourhood (e.g., Fort, Kollupitiya/Bambalapitiya, Cinnamon Gardens).

Which would you prefer?