What's your budget?
Generally, you can't go far wrong with Ibanez for the money when it comes to extended range. One thing to be conscious of, some 6ers have very narrow string spacing so, if that's something you're sensitive to, ask before you buy. Ibanez SRs have narrow spacing, around 16mm at the bridge whereas the BTBs have a more traditional 19mm. Years ago I went from 4 straight up to 6 with an SR and the narrow string spacing took a long time to adjust to.
For fretless, personally, I'd go for a decent 4 string with a rosewood fretboard and take the frets out. Easy to do and rosewood is my favourite fretless wood. Avoid basses with narrow necks if you do go down this route, the likes of a SR are super narrow if you remove the frets, uncomfortably so. My current fretless is a defretted Jazz type. Simple and you can't go wrong. Plus, the side dots are in the place I'm used to. With a lot of factory fretlesses, the side dots are where the 3rd, 5th, 7th, etc frets would be, not where you're used to them being, between the frets. It did my head in going between fretted and fretless and the fucking dots moving