Bear in mind, small Valve amps are not quiet at all.
As you're aware, 100/150 watt valve amps are made not for volume, but so people don't even have to turn them up all the way so they have plenty of headroom.
Yes, a 5 watt valve junior is not as loud as any 100 watt head with external cab, true, but you're going to be massively disappointed if you buy one with the expectation of being able to crank the power amp so it sounds rich and juicy and have it still be quiet.
5 watts is half the volume of 50 watts, and 50 watts is LOUD in tube amp terms. 5 watts is loud enough to still cause you plenty of good ear damage.
I remember a while ago playing a Mesa Boogie Lone Star Special class A amp, on the 5 watt mode. I shit you not I could not turn the master volume over about 3 without having someone tell me that it was too loud.
Basically, in essence, lower wattage valve amps are for people who know their shit about amps and want an amp with lower headroom. They were not designed and are not intended for home practice.
You're looking at either buying an attenuator, or seeking an amp with less than 1 watt if you want juicy valve power amp vibes without scaring the shit outta your kid.
Otherwise, look into solid state options.