How do i change the font style of wordpress without changing the theme?

or can anyone recommend some lovely themes that has a nice interface, page buttons and is quite customisable?

Edit the CSS file, you can even import your own font using @ font-face.

You can use google web font

what theme are you on now?
usually in sidebar, the theme has a customization tab where you can play with colors, appearance, font things like that.
otherwise simply google "change wordpress theme font" and youll be met with several tutorials covering the different ways to do it, including the way mentioned above.

if you want a theme recommended let us know little more about your project. is it a blog. an agency. a mechanic business. etc.
usually i visit themelock.com > search my kw > skim through the demo's until something stands out to me