If yours is a wall mount W/C with concealed cistern, 95% u r gona get P-Trap w/c.
HDBs floor mount are all S-Traps.
Whichever shops u go always 1st measure from your wall finishing to the centre of your w/c pipe coming out of the floor is how much. Cause you dun Wan be getting a floor mount w/c with different dimension.
example: u buy a floor mount w/c from w/c cistern back to centre of discharge pipe is 250. U go home u measure and realise yours is 350. So ya hope u understand.