I was in Wales for about 2 weeks last summer. No car, train and bus only.
I stayed in Llandudno. There are many places to stay there with sea views. I chose the Bromwell Court and used it as a home base to visit other places including Conwy. There is free street parking right in front. The breakfast was great and the location very convenient for me. Here's the link: https://www.bromwellcourt.co.uk/index.html
I'm not a big fan of castles, so I didn't visit the one in Conwy. My favorite thing there was Plas Mawr, described as "finest surviving Elizabethan town house anywhere in Britain." It was so much fun to walk through and not at all crowded. Here's the link: https://cadw.gov.wales/visit/places-to-visit/plas-mawr?lang=en
The other place I visited was the Smallest House in Great Britain. I must admit that this sounded like something too touristy for me, but I changed my mind at the bus stop near my B&B in Llandudno. I met a woman there who was also going to Conwy. She had recently retired at the age of 60, gotten bored being home so much and was working at the Smallest House 2 afternoons each week. What luck! When we got off the bus in Conwy, she walked me to Plas Mawr.
After I finished there, I walked around town a bit and ended up at the Smallest House. The short line moved quickly. She took my picture with my arms stretched out. My fingertips almost reached to the far edges of the place. More fun. Here's the link: http://www.thesmallesthouse.co.uk/
Before catching the bus back to Llandudno, I had a great meal at the Erskine Arms, a place she recommended. They also have rooms. Here's the link: https://erskinearms.co.uk/
I spent a few nights in the Premier Inn in Aberystwyth. It's in a very convenient location near the water. The breakfast was great, and they have guest parking.
My main reason for staying in Aberystwyth was to take the steam train to Devils Bridge. It was a several block walk from the hotel and they have lots of parking so you might want to drive. I just walked up and bought a ticket. It was great fun. There were people on the train with dogs. I loved that. Some on the train were getting on and off the train to hike. Note that there are toilets where you get on the train and where you get off at the top. There are none at any of the stops along the way. There are snacks where you get on as well as a nice cafe at the top. Also note that if you ride in one of the open cars, you may get a little soot on your clothes. This is the link to the Vale of Rheidol Railway: https://www.rheidolrailway.co.uk/
I stayed at the lovely Ramsey House in St. David's: https://www.ramseyhouse.co.uk/
It's a few blocks out of town but has parking, easy walking access to hikes and walks in the area and to the amazing St. David's Cathedral: https://www.stdavidscathedral.org.uk/visit-us
I hope this wasn't TMI and that it might help you with your planning. I'd never been to Wales before. After I got home, I learned I have 8% Welsh heritage. 🏴