Paint fix the worn things
Here are a few ideas Kelly! https://gorving.ca/blog/6-ways-make-rv-super-cozy/
Trailer as in mobile home or camper?
The best made over campers I have seen started with paint. I would start with that and then go into flooring. https://mountainmodernlife.com/beach-worthy-boho-rv-renovation/
Switch out all bulbs to LED or replace older more harsh light fixtures with integrated fixtures. Installing dimmer switches on all lights and lamp cords will allow for softer, cozier light that can be adjusted easily according to time or day or seasons.
Number 1 requested item in my area by my disabled clients is new flooring, switch to LVP plank flooring from carpeting makes keeping it clean much easier. Add area rugs you can shake out or wash.
Second most requested item is curtains to keep in the warmth, this means sewing covers with Reflextix double reflective insulation..... https://www.homedepot.com/p/Reflectix-24-in-x-25-ft-Double-Reflective-Insulation-Roll-with-Staple-Tab-Edge-ST24025/100020855?MERCH=REC-_-pipsem-_-202092205-_-100020855-_-N you can find directions on YouTube
Third is to put a layer of 1 1/2" rigid foam insulation along the bottom of the trailer to keep out the cold and wind. https://www.trailmeister.com/trailer-insulation/
You might be able to get some financial assistance to change out your windows to double paned, check with your local PUD company.
A couple of years ago I helped my sister and her husband renovate their trailer. It turned out amazing! We painted the walls and put down wood flooring then added warm cozy rugs throughout the house, curtains and accessories. An inexpensive and easy way to add curtains is to use dropcloths. Here is a DIY. https://www.hometalk.com/37018290/how-to-make-no-sew-bleached-drop-cloth-curtains