Hi and welcome to the board. We'll be happy to help, but we need a bit more info before we can. What is it, exactly, that you want your tank to do? What kind of tank are you vaping now, and is it making good vapor for you? Is your Siggie the Temp Control model, or straight wattage? If the former, do you want to use TC? What is the PG/VG ratio you're likely to use? All of these, and more, will make a difference as to what we will recommend. One thing-- make that two things-- to remember: having a high- watt mod doesn't mean you have to run it wide open all the time. I'm holding a 60W mod as I type, with a Kanthal build of .5 on it, and I've got it set for 17 watts. At home I have a 200 W machine, currently set up for Temp Control, and it's limited out at 40 W. And the other thing is you're unlikely to find pre-made coils rated much in excess of 100W, and only a few that tall. Really high watts is kind of an RBA thing.
Edit: I forgot to add a good, flexible starter, so you can figure out what you want to do, is a Kanger Subtank. It has +Ohm and subohm coils, and a rebuild deck. That way you can experiment some. It won't run at 150 watts, though...