Itinerary suggestions for 30 yr old couple in early March

Hello everybody, Me and my wife will have a 17 night stay in Thailand starting with February 27th. Current plan is to enjoy Bangkok for 3 days, and then go to the island/beach area - 5-6 days Krabi, maybe phi phi islands for 2-3 days and then 4 days at a nicer resort, probably on Koh Samui (open to suggestions here)

We enjoy sightseeing, food (street food and restaurants are usually our trip highlights), boat trips, beaches, and just walking around. No real interest in nightlife.

Would love your recommendations/tips on the itinerary we thought out. We haven't really bought anything else but the plane tickets, so we are open to changing it.

Regarding resorts, any recommendation for nice beachfront places around 150 EUR per night? Have seen Koh Samui is a place with many fancy resorts.

Where do you recommend we stay in Bangkok? We usually just sleep and rest at the hotel, so we would prefer a cheaper, but with a nice location hotel, close to the public transport lines. Somewhere safe in the city, closer to the locals rather than the main tourist area. Would love to just stumble into nice restaurants in any direction we go from the hotel.

Thanks!