Stern Gear Options

What is the best option for stern gear please to keep vibration to a minimum (assuming correct alignment and the 3/4" shaft is straight)?
My engine is on flexible mounts and there is very little vibration when idling.  I have the usual cutless bearing at the prop end; and the stern tube ends at a mini bulkhead (it does not protrude through the bulkhead towards the engine).
Bolted to the bulkhead is a rigid stern gland with a flange and there is an R&D coupling at the gearbox end. I have a lot of vibration when above 2000 engine rpm which could be due to many causes of course and this winter I want to remove and check everything and, if necessary replace to achieve a good setup. I always think the R&D is not flexible enough, particularly with the CO26's long shaft. It just seems like a lump of hard plastic to me - but I could be wrong.
I'm considering having a rigid coupling at the gearbox and a flexible (i.e. with a short hose), flanged stern gland. As I'm fiscally challenged a posh set up with two cv joints and a thrust bearing is out of my range. 
I would be very grateful for your thoughts. Thank you.