Has anyone sailed (ocean or river) on a ship with a comfortable sleeping fir 3 adults?
All lower beds, no upper berth.

I know Regent Seven Seas and Oceania have ships that have multi-bedroom suites that can sleep 3 or 4 people and I’m pretty sure many of the other medium to large ship cruise lines offer similar accommodations. You’ll pay dearly for these suites as they are usually the largest accommodations on board.

Also, many cruise lines have ships that have “adjoining” staterooms that can accommodate up to 4 people. You’ll have to book and pay for both rooms to get this feature.

If you are looking for more budget friendly accommodations with 3 people in a typical stateroom that normally is for 2 people then the best you can hope for is a cot or folding bed that can be set up each evening.

We have sailed on several different Norwegian Cruise Line ships in Haven cabins which have two bedrooms and two bathrooms; also in Royal cabins and Celebrity cabins which have full second bathrooms and sofabeds in separate areas.

In checking around we found that Azamara has cabins with a small sofa that makes
into a bed so we could sleep 3 in a cabin. Actually we were looking for a smaller
ship as we are not fans of the mega ships.

Granted it would be tight quarters but at least we could be together. Now we just have to see
if they will actually sail in Sept/Oct or if Covid will still prevail.

Haven't done this yet due to traveling only with DH. Planning a cruise for June 2022 for three long-time friends (over half a century). Booked a balcony cabin, hoping to give us a bit more room to spread out. The cabin has twin beds and a sofa bed. The weather should be warm throughout.

We did that once and never again. It's not just the sleeping arrangements. Think of three people getting ready and only one SMALL bathroom.

Many sofa beds are uncomfortable. The same person should not be stuck on the sofa bed the entire cruise.

I agree with schmerl. Why not just book adjoining cabins? Or a balcony room, and then a standard (even inside) room. Then you can hang out together in the nice room/balcony but have a second bathroom and an option for shifting one person to the single occupancy room if you have a snorer or someone needs some alone time.

I can't even imagine three people sharing a tiny cruise cabin bathroom.

I would not automatically dismiss the Haven which is a cruise ship within a cruise ship.

We had a sofa bed on one cruise. It was not a sofa as you might think of it. It was a frame with a twin size mattress that folded. It was as comfortable as the other beds. The pull downs were also twin size, regular mattresses, the same as on the regular beds. As to a balcony, though we had the outside space for sitting, which was nice, because of the arrangement of the beds, there seemed to be less room to move around inside the cabin. Check interior cabin size.

I recall these tips from Cruise Critic:
Check if this is still available -- on most cruise lines you can ask the cabin steward for a foam mattress topper for your bed. This can be useful for the sofa bed.
Another tip for those with more than 2 people in a cabin was to use the shower facilities in the gym or spa area.