Speaker question

I recently got a pair of Linn Majik 109 speakers. I fell in love with the sound when I auditioned them and they were in my price range. They also fit my bookshelf space. I have enjoyed them without any subwoofer. I use an older Linn power amp.
Now I find myself remodeling my listening room and entertainment center. I may have more room for a slightly larger speaker. I still cannot get a floor standing speaker, though.
Does anyone have any thoughts about a somewhat larger speaker that may be able to provide somewhat more of the low end, yet still sit on a shelf?
I have some Paradigm Reference Studio 40s that have very good bass for their compact size. I am sure there are other speakers that are better, but I can recomend these from personal experience.
More low end without increasing size will require you to live with lower sensitivity which will require more amplifier power to hit the same sound pressure levels. That's just the physics of speaker enclosures.
Try adding a small M&K KX10 sub or two. I did that when I had the Majik 140's when I wanted more bass. I now use the subs with Lipinski L707's. You can actually get those combos sounding like just one speaker. The 109's are nice, so enjoy them.
The Linn LK100 power amp seems now to give me sufficient power. (I used to have Linn Keilidh speakers and they were powered well for my needs.) I am wondering if a new bookshelf speaker that reached somewhat lower might be better for me now, since I have more room to utilize.
It all depends on how much larger an enclosure you can fit there, and how much sensitivity you're willing to sacrifice.

Just keep in mind that it doesn't take much of a loss in sensitivity to require the amp to reach its peak output on transients (clipping). It might make more sense to add a small powered sub or two that can also fit on the shelf and keep the bookshelf speakers that have served you well up until now.
I like the Sub idea. Will I be better off adding a small powered sub to my LInns than getting a slightly bigger speaker, such as a B & W CM5 and not having a sub?
Two benefits from adding small subs.

You can high pass the monitors and relieve the woofers of deep bass duty which will clean up the mids and allow your amp to deliver more power without clipping (provided you high pass the signal to the amp).

The second benefit is that using subs allows you to place them in locations that maximize bass performance and response smoothness which might not be where the monitors are best located. A slightly larger monitor will not do for you what a couple of small subs will add.
I have a listening room that is around 11' x 19'. I generally listen to jazz and vocals and classical. No rock. Can I get by with one subwoofer? Or do I absolutely need two of them?
You could probably get away with a single sub, especially if you always listen in the same spot. You would simply move the sub around until you find the position that gives you the best overall sound.