We have cruised before with Thomsons on both Majesty and Celebration as well as cruising with P&O ships so consider ourselves to be seasoned cruisers. My friend is wheelchair bound (standard chair not electric) and is unable to get out of it even for a few step. This has never stopped us cruising.
We have always had wonderful help from the crew embarking/disembarking, and from the Destination service teams in informing us what we could do at each port and assisting us to be independent, While we would love to go on some of the tours, unfortunately we have never found a tour bus which allowed wheelchair access. So with guidance we do our own thing and thoroughly enjoy our cruise.
Sadly our cruise with Thomson Dream was actually a nightmare. Don't take me wrong, we loved the ship and the crew couldn't have helped anymore if they tried, the ports weren't the best but we knew that before going, BUT...
Spacious and clean, although the bathroom was NOT wheelchair friendly. It would be fine for someone who could get out of the chair and walk a few steps but not for someone needing to take their chair into it.