The Beethoven to me is technically easier to tackle and I'd guess it would be similar to Traumerei although I haven't played the latter. You could also have a look at Beethoven's "easy" sonatas, Op.49/1 and 49/2 which could give you a nice "boost" in a few more technical aspects. 
I'm also in agreement. Yes, it's not as though the Clair de Lune movement (or, say, one of the Arabesques) could not be played, but I suspect that could lead to more frustration at your stage. Although you seem to have a strong work ethic, so I couldn't really say for sure. Just depends how much effort you want to put into it, and especially how strong your arpeggios are (for both the Suite Bergamesque movement and for the second Arabesque (or "Arabesk"): about the latter, as well as the former, it just depends if you're up to playing two against three and some variations, in addition to the notes.
We could talk about Brahms all day when it comes to similar challenges.
Very hard to say without knowing more about your mechanical or musical ability.
The Beethoven movement from the Pathétique is a good choice, although that will present some novel challenges. There's plenty of Beethoven slow movements from the middle period that can be played with even less difficulty, but I'd recommend just reading through them and finding what speaks to you and go for it.
If the Pathétique Ab major movement speaks to you, you should give it a shot, but I wouldn't underestimate it, in that it's not exactly a completely trivial or easy piece. Relatively speaking, you know.
You will learn a lot in the process, though. It's more difficult than the Schumann Träumerei, but not impossible if you can handle bringing out the melody in one hand while simultaneously performing accompaniment in the same hand.
Also, kind of a slow, almost meditative piece, the first movement from Op. 27 no. 1 (not the "Moonlight" but the sonata that precedes it in the same opus number). It's fairly substantial in length, but not difficult at all, especially if you are comfortable running scales smoothly in the LH. I think András Schiff compared it in one of his lectures on the sonatas from the UK to a kind of lullaby-type piece.
As well as from the Op 126 Bagatelles (a few of those are a bit tricky, but you can certainly work through at least a few of them without too much trouble). Perhaps the very last one from the set you might find affinity with, and can play with a bit of effort. Probably about the same difficulty as the Pathétique slow movement (don't be frightened by the very fast little flourish at the beginning and end [just omit it if you like: it's just a brief scalar passage built around the authentic cadence...doesn't matter IMHO] most of the piece is rather slow and contemplative, with some interesting harmonies). And the second-to-last one in the set you can play, as well as the first, perhaps some of the others. The First one and the Fifth one are probably the easiest of the set, and have a simple, almost rustic feel to them (yes, the first one has a couple of fast scalar runs in the RH, but if you're not up to that, the piano police won't come for you if you play them at a speed you can do: they're just little flourishes, more or less to épater les bourgeois!)
Good recommendations above about alternate pieces from Debussy. I personally find the slower works of Debussy to be challenging in a musical sense, but the notes themselves are not necessarily very difficult. Or if you really want slow, evocative, and a bit odd from Debussy, there's "Jimbo's Lullaby" from the "Children's Corner" suite, but it is a pretty strange little work. I know some people find it a bit strange, but I like it, and you could certainly play it. The precise rhythm would be the main technical challenge. Quite a few choices should be available to you from the préludes and fit your tastes.
TBH while I...what do they call it in English, "The girl with the flaxen hair," I believe it's a marvelous piece, it's almost deceptive IMHO. Yes, any child (the suite is not written to played by children, as such, but rather to amuse Debussy's sense of childhood reveries) can play the notes, but I find it complicated to make coherent music out of.
If you want something a bit different, there are a great many slower pieces scattered throughout Bach's suites and elsewhere. For example, for a very well-known piece which you can play, just the Aria from the Goldberg Variations would fit the bill pretty well. You might not choose to play it at the fairly brisk tempo from Gould's first recording of it, but, then again, you might. You have some options there for interpretation.
Also an ideal choice for doing some metronome work if you find your performance becomes a bit sluggish at times, but it's just as likely you'd have no trouble with it at all. Good opportunity to work on subdividing if you find that's necessary. That simple piece as well has its own little challenges, but nothing you couldn't handle. No, I don't recommend using pedal on it, but if it's necessary to connect the bass motion in the second "half" of the aria, then so be it.
The audience need never know!
And, yes, there are several of the variations which don't feature the kind of brutal dual-manual stacked clavichord scale running, which you can also play, but I'd start with the Aria first. In whatever fashion you like it. Yes, you'd have a number of decisions to make, about tempo, ornamentation, and so forth, but that's most of the fun of being a musician, no?
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