push pull or single ended

Nelson Pass First Watt F2 class A SS amps are also a good choice.

Nice idea, I agree, go Push Pull.

Your efficient speakers means you can easily stay in the 25-30-35 wpc power range. That gives you lots of options, lots of competition there.

new, used, vintage.

Having return options is a great means to success.

As mentioned: less power = less weight; less heat; more placement options.

.........................................

some things to be aware of while searching:

a. Some new tube amps, like my Cayin offer two modes of operation: i.e. 22 wpc in Triode Mode or 45 wpc in ultra-linear mode. Not needed, just mentioning it. I and all my friends prefer the more common ultra-linear mode. It’s not really the additional power (especially with efficient speakers), the sound is different, some like Triode for certain types of music and Ultra-Linear for other music.

b. You will discover ’tube rolling’. i.e. my amp can use either 6550 power tubes or KT88 tubes. It came with 6550’s, very nice. After a while, I tried KT88’s. I prefer the KT88’s. The bias for KT88’s is different that for 6550’s, that is a good reason to have easy external bias control.

c. Many tube amps offer easy external Bias control, with external adjusters and meters, I wish my amp had that.

An OTL amp was mentioned. After decades as a die hard SET guy, I am now a dedicated Atma-Sphere guy. The Atmas give the detail of a fine SS amp with the musicality of a great SET. The entry level S-30 would be the amp for you. All Atma amps are equally good. The only difference is power and price. Atma’s Ralph Karsten uses a S-30 in his system.

+1 for the S-30. Super reliable and easy to use. M60s would offer more flexibility if you ever changed speakers, but at a higher price. Sonic character is similar if you happen upon M60 reviews, and are wondering if those comments would apply. 
I  agree that SET would be more of a transition, IMHO OTL gives you the best of both if paired with compatible speakers. Cheers,
Spencer 

@injr  Are you using an electronic crossover? If not the efficiency of your speakers will be a problem with most SETs.