@knagelli, I second the use of ET as a large and reliable *A parter who have plenty of options through ADD. Their J product was fine from BKK when I flew it in Sep last year. Not SQ individual seats level J, but more than comfortable enough for my needs.
I had booked a decent value ET J airfare BKK-ADD-CAI return and had used SQ Y+ for the connecting flights from Australia to/from BKK. All were being credited to my TK *A account. Watch out for some of the fare buckets in case they’re non-crediting to SQ, which I assume is your aim.
@Grrr, if you can find a longer layover in ADD, I’d go for that. ET will give you a free hotel for the stopover, including transfer and meals if the timing is over main meal periods. I don’t know if 7.5 hours would be long enough for the hotel as you’d really only end up with three hours of sleep time. I deliberately booked a long layover in ADD as I wanted to go and see a bit of the city. Was put up at the Ethiopian Skylight hotel near the airport and it’s nice. Transfer was via minibus to/from the airport. ADD ET lounge is nothing great and because they tend to bank their flights, it’s generally quite busy.

ET B787 J seating. 2-2-2, but they are lie flat.

Transfer shuttle at ADD to Ethiopian Skylight hotel. Was easy to find and I had no wait.

Hotel restaurant where I had two of my three complimentary meals during the layover. I didn’t have lunch there as I’d caught a taxi from the hotel elsewhere during the day. Nothing special, just a buffet, but was mostly Ethiopian food and hit the spot.

They even did this smoking of incense thing which was different, but not unpleasant. I saw (and smelt) the same thing, just inside the entrance to the ET lounge at ADD.

ADD gate and concourse area at 2130 local time during a bank of flight departures.
I’ve just seen in that last pic the sign showing a Skylight hotel in the terminal. That might be a better option for a shorter layover!