"Addition of subwoofer to Music System"

I retired 20 years ago, and have since downsized my audio system to a more modest one consisting of Monitor Audio Gold 100 speakers on Monitor Audio Stands, a Marantz CD player, Rotel Integrated Amp with good DAC, Linn Basik turntable with Akito tonearm and Rega Exacta 2 cartridge, Panamax power conditioner, Kimber Cables and Interconnects, and PS Audio power cables from CD and Amp. I have a large music collection; 1500 vinyls, 3000 CDs and 2500 in AIFF files on separate hard drive on Mac. I would like to add subwoofer to my audio system and I am looking for suggestions and recommendations on cost effective subwoofers. This is strictly an audio system, no video. It does have a whole house component with KEF in wall speakers being run through a Denon AV receiver that is mainly used for background. My room is moderate 13 x 25 with 8 feet ceiling. I listen mainly to jazz, classical, country and R&B. Very little hard rock. Prefer CD format. I don't need booming bass and prefer clean sound at moderate listening levels. Would love to hear your suggestions based upon experience. Many thanks.