It sounds like you have a lot of experience with pipe organs, in which case I'm guessing you want more than just the sound. There are plenty of keyboards with organ sounds built in (of varying quality...), but these are normally based around a piano layout, which is obviously unsuitable for "serious" organ playing. Most of them will allow you to plug in footpedals and have an effect which approximates the swell pedal.
Most keyboards attempting to emulate a pipe organ fully (with multiple manuals etc) are generally serious pieces of furniture. They do generally feature a fairly traditional layout of manuals and stops, but in terms of dimensions have more in common with an upright piano. I'm no expert on their sounds, but my instinct would be to go with the Nord as it's small, lightweight and Nord has an excellent reputation at emulating acoustic instruments.