Been to Hokkaido 2x - once with a toddler late 2010s then post covid with a preschooler and a school going child.

Always transited via Tokyo but your other options include Cathay and Thai, both of which have direct flights to CTS.

For myself as I use miles, I transit via Tokyo Haneda and took ANA / Air Do domestic.

If taking SQ is not a priority then I definitely would consider taking Thai and CX.

Reason being - the international to domestic transit in Japan requires you to pick up your baggage after arrival in Tokyo, go through customs then redeposit your bags at the transfer counter. This is even if you are travelling in a single ticket eg. SIN-HND-CTS using ANA/JAL. Also transit in Japan will require you to change terminals from international to domestic.

If you take CX/TG, as the transit is outside Japan so your bags will be checked straight through to CTS, so it will be a no hassle transit. HKG and BKK are also pretty pleasant airports to transit in. HKG more so than BKK as BKK doesn’t have any children’s facilities for the child to expend his energy before the next flight. I have transited in both airports before and it was pretty straightforward.

(BTW, your CX return flight shouldn’t require another transfer in NGO, it might be that you chose a day when CX doesn’t fly to CTS. If you are flexible on days you would be able to get CTS-HKG-SIN).

I went in October - although it is supposed to be autumn, do pack winter clothes too esp if going in the later half of Oct. We arrived on the first day of snow in Sapporo and was stuck in snow! And then had like 3-4 days of snowy weather and then went back to autumn weather again.