I would stay as close to Soi Twilight as you can so you are within a short walking distance of MANY establishments. Then I would go EARLY to one of the more popular bars(get a map beforehand- and consider Hot Male and Dream Boy) and talk to the "mammasan" and tell them EXACTLY what your preference is showing them 100-200 baht tip and ask them to recommend someone. Imply you plan to return as your hotel is nearby. Pick your guy and confirm with the help of the "mammasan" that he will do what you wish. Off you go.
If you are happy with him, then negotiate with him to stay longer, If not 100% happy, return to same bar and try again.
I recommend the above approach because 1) you save time and taxi, 2) "mammasans" at better bars CAN sometimes be helpful if you are polite, tip and tell them you want their help, 3) it is more economical to have a barboy back to the room than from most massage shops, 4) if your primary goal is sex over massage I think the bar route is a better use of time, because you will have time to go back to the bar and repeat, and 5) you have a wide selection of bars all next to one another.
Smile and be very polite when you go to the bars.
Let us know how it works out.