Datasets with only single feature variable
Finding a dataset with just two variables might be difficult because these would be a very naive dataset.

Therefore, what I would suggest, is for your to take a more complex dataset and pick two columns that you would like to analyse.

For example, you could look at this dataset: https://www.kaggle.com/sohier/calcofi#bottle.csv

Then, pick the column Depthm as your feature variable and the column T_degC are your target variable. These two columns seem to match the type of data that you expect.

Here is how these two variables look like (for Depthm &gt; 2000)



or you could look at  another two variables instead, for example Depthm vs Salnty: