"Can you recommend ... a filter that i can use inside so I won't even need a flash in those situations."
What film are you using?
You can get tungsten-balanced film that will not have anything like as much of an orange colour cast when used indoors with incandescent (tungsten) lamps. The only tungsten balanced colour film intended for still cameras is reversal (ie slide) film. 35 mm tungsten negative still film was discontinued by Kodak not so long ago. You can get 500 speed tungsten negative film for movie cameras, and it will work in your Pentax if loaded into a cassette, but there are few places that will process it at reasonable cost.
However, you can use daylight colour negative film without a filter. It can be corrected at the printing stage. If you overexpose two stops it will be easier to correct - ie if you are using ISO 800 film set your meter to 200. You could also set it to 400, or anywhere in between 200 and 800. There are a range of possibilities, sliding between full correction and low film speed to less-than-perfect correction in the shadows and full film speed.
A deep blue filter to convert tungsten to daylight will lose two stops of light. A Wratten 80A is about right. If you are using colour negative film I suggest that you start by overexposing one of the ISO 800 or ISO 1600 films by one stop and see how the results come out.
This is just a start. There are so many ways of doing this that it could be confusing to go through them all at once. Please ask questions if anything is unclear - I have kept this very basic to start with.
Best,
Helen