The biggest thrill in this game though is playing together with others for a lot of people, interacting working together with others to do something, or even playing against one another in an honorable way : PvP (not PK).
Other great fun for solo players is develop a personal skill at something : Decorating a house, organizing your belongings so you know what is where, making nice designs, becoming good at lead taming or taming in general just for the fun of it..Or develop a hobby, such as collecting things you like, like rare pets, or spawning some creatures to eventually spawn a rare colored pet, keep it or make some gold that way. (Tame and sell a 4 slot dragon, tame a rare color Cusidhe, a pure white, a black, or a Blaze one! etc.). Fishing can be a blast for some players that solo, and there is a huge Fishing update with new rewards and challenges coming up shortly. Do a Fel spawn, aspire to get PS and sell for UO $, get rare items etc. And dont be afraid to get attacked by PKs. Become a guild member in a nice guild that is active, give it a chance and if you dont like it quit the guild. Start a toon in Siege, great player base, close-knit community, may surprise you. If you are a crafter your services will be priceless there. You can hunt scripter bots actively, and do a lot of good for the game also. A million things to do. What shard are you on?
Sounds like you boxed yourself in a one-mode routine, and you may be repeating it each time. Same thing over and over again, each play day. If you have the time, it is difficult to get bored in this game. The content is massive, and there is new content coming up in just a few months.
Finally, don't be bashful. Talk to people in game. You may be surprized how many good people there are.
We all know that the pixels in UO are not the best in the present day games but, UO has a nicer player base, and people here are mostly mature. Don't let a few rotten apples spoil it for you..Create your own fun, discover other people, and different things in UO, and most importantly have fun!