What you are looking for does exist and can sound superb with your speakers.
KR Kronzilla's would be an interesting choice. The tube is esoteric but it sounds really good and delivers a lot of power. Not exactly like a 300B but 300Bish. KR also makes a 40w 300B push pull.
Alternative options that would be intriguing would be the Art Audio Quartets (845 push pull) and Opus 4 (Kt88 push pull) that deliver a very engaging experience. They both use a small amount of negative feedback. These are both 45w in triode. Michael Bump did a review of the Quartets a few years ago. Bob Grossman recently did a review of the Opus 4s. Both for Enjoy the Music.
The CANOR Virtus M1 monos are a KT150 based amp that is switchable between 0dB of negative feedback and 6dB. They also allow for switching to Ultralinear and are 110w in that mode. Several reviews have been done in Europe on these amps.
Aries Cerat makes a few amps that are higher power and deliver what you are looking for. The Concero 65 is parallel SET running the 813 tube. The Essentia is a SS Amp that sounds very much like a SET and could do a nice job.
None of these are inexpensive but all are stunningly good amps and will do okay with your speakers in that smallish room. They either have 4ohm taps or in the case of the Essentia are stable to 1 Ohm.
Full disclosure, I am a dealer for all these brands. That said, it also means I have tested these amps in the real world. I have publicly shown speakers as low as 84dB sensitivity in rooms about your size with the Art Audio and Canor amps and have heard the Kronzilla and ACs in similar spaces.
You could also go with a more traditional design like VAC or a hybrid design from a brand like Riviera. Any of these will shine like the sun with those speakers.