Some of the better hotels nearby t21,
grande centerpoint terminal 21 - linked to t21 ...
price about 150+
pullman bangkok grande sukhumvit (formerly grand grand millennium)
price about 180+
others includes sheraton grande sukhuvmit, westin grande sukvhumit ...
if you want 4* below 100sgd per nite, can try jasmine city superior 34m2, admiral premier superior 32m2, within 7 minutes walk from t21 ...
if you are into the hotel breakfast, and dont mind the 7 to 10 min walk to bts chitlom, and the 3 bts stations to bts asoke, then amari watergate is good
if you prefer to stay nearby t21, dun mind the higher price , then the above few hotels mentioned might be a good choice ...