Snow and frost in the south of England is about as common as Denmark beating Spain in football. It just doesn't happen.
Playing slow tunes can be hard work since the internal metronome ticks too slowly to give you a steady time reference. The standard approach is to subdivide the beat but in practice it is hugely distracting to have to count all the time, and even worse, you can be 'right', and the others 'wrong', but you are the one who ends up sounding out of place because you are relying on a virtual metronome that only you can hear whereas the others are playing together. Coping with slow tempos in jazz is really a matter of feel rather than time.
My choices of tunes for this section are slightly off the beaten track.
The use of altered chords in Blue In Green (mp3) by Miles Davis gives it a dark, moody sound. The sparse melody is carefully constructed to hit the notes that define the sound of the chords. The opening note, for example, is the #11 in the Bbmaj7 chord.
Wayne Shorter's Infant Eyes (mp3) is equally dark but it has a more modern sound to it. It has been covered by several fusion-oriented artists, including guitarist John Etheridge and Canadian band Uzeb.
To lighten things up a bit, here is A Child Is Born (mp3), a happy uncomplicated ballad in 3/4, by Thad Jones. The melody is based on a simple theme that is played four times. The chord sequence is different for each repetition of the melody. In this tune the variation is in the chords, not the melody.
The use of dynamics is very effective for giving your playing a calm and relaxed mood. Drummers use so-called 'ghost notes' to prevent their playing from coming across as too overwhelming (with the possible exception of rock drummers, who tend to like it non-stop loud). The same technique can be used on the guitar. In a ballad it is nice to hear certain notes and chords only as a kind of backdrop. The main action is subtle as it is, and putting a quiet 'second layer' beneath it often works well.