Small - smaller - the smallest
tall - taller - the tallest
old - older/elder - the oldest/the eldest
old-fashioned - more old-fashioned - the most old-fashioned
messy - messier - the messiest
light - lighter - the lightest
clean - cleaner - the cleanest
colourful - more colourful - the most colourful
comfortable - more comfortable - the most comfortable
large - larger - the largest
modern - moderner/more modern - modernest/the most modern
bad - worse - worst
thin - thinner - the thinnest
fat - fatter - the fattest
good - better - the best