Perhaps you could provide some clarity to these areas in order to get some useful advice:
1. Bangkok vs Beach
Two very different types of holiday and two very different types of activities to unwind - how will you want to unwind?
2. Titanium Benefits vs Cheap Room
You mention you are Titanium which implies you're looking for elite benefits. You'll only get free food and booze in lounges in Bangkok. You'll get free breakfasts at beach resorts. If you're looking for best lounge benefits in Bangkok then there's a thread that already covers this. So how are you defining "good value"? Certainly, you'll not be heading to any Bonvoy hotel on Samui. If you're not after lounge benefits then value would equate directly to price which the Marriott web site can help you with for your dates.
3. Kitchenette in a Hotel Room
This is the deal-breaker when it comes to Bonvoy hotels in Thailand. As has been pointed out there are some executive apartments in Bangkok but that's about it. Food in Thailand is good and cheap and Bonvoy hotels really do not address self-catering. So, if you must cook for yourself, store food, and reheat it then you're looking at booking an AirBNB or similar which will be cheaper anyway and your Bonvoy status would be irrelevent.
If you don't know Thailand then I'd suggest in a week you spend 2-3 nights in Bangkok at a hotel with a decent lounge for that experience (specific hotel and location depends on what flavour of nightlife you're likely to want) and the rest of it at a beach resort. For the resort you have to decide if you want to be isolated (example value location Le Meridien Khao Lak) or near some night activity (example value location: Four Points Patong or Marriott Hua Hin). The best value Bonvoy hotels I've found are the all inclusive packages at Le Meridien Khao Lak and even better the Phuket Marriott Merlin Beach where storing and reheating food is especially irrelevant because you can eat what you like when you like.