I found that Nos12sn7 tubes are available at lower price.
But I like full and sweet sound out of 6sn7.
Did you change the filament voltage on the amp concerned to suit the12SN7? All other things being equal, the filament voltage shouldn’t make the slightest bit of difference to the sound. You were hearing the difference between the tube types, not the difference between absolutely otherwise identical tubes using different filament voltages.
To make a sweeping statement that 6SN7 tubes are ‘fuller and sweeter’ than 12SN7s, or 8SN7s for that matter matter without conducting a series of tests using controlled samples is simply not credible.