Since we're both in the poorhouse these days, I'll just greet you this a.m. with, "Howdy neighbor!" I feel your pain in terms of wanting to try lots of gear that's out of reach, at least for now. I do have a little bit of a theory on that K 90 since you sound like you had a good experience with it.
If you only used that frame once or twice and it gave you a tired arm with no elbow discomfort, you may be able to get more used to playing with it as you evolve your strokes and make more energy with your legs and your core muscles. I took a leap of faith with some really heavy mids a couple of years ago to help train my strokes into better shape. They gave me that tired arm until I developed a better progression in my strokes from the legs up. I don't recommend this for everyone (there is such a thing as too heavy), but I don't think it's a completely perilous thing to take up with a racquet that has some more weight if you honestly think you can learn to use it and have fun with it. It just requires some dedication.
It might be a reasonable course just because your elbow agreed with that K pretty well. If you don't want to go quite as hefty as the "Fed stick", there are the other ProStaffs in the 6.1/Six-One line that may work well and you might even score an older model with a nice low price tag. I get a lot of comfort these days with my Volkl C10's which have a bit more flex than my old 6.1 Classics. These are up in that 12+ oz. weight range, but their head-light balance of around 10 points makes them easy to handle for me. I found more confidence at the baseline with these frames as soon as I got them, too.
Other hefty frames that seem to have some comfort built in include the TW edition of the Donnay Pro One along with the 10 series from Volkl and the 11 series from Boris Becker. Prince has an interesting array of racquets and something like their Ozone Tour or heavier Ozone Pro Tour could be a plush hitter for a baseliner. I know that they're not cheap, but these are some good examples. Oh yeah - the Yonex RQiS 1 Tour was an odd surprise. I think it weighs in at a little under 12 oz., but it has a great combination of crisp and cozy feel. Quite comfortable for a not-so-heavy racquet.