bequem
comfortable
Providing a feeling of physical well-being and relaxation; not restrictive or tiring.
Dieser Sessel ist sehr bequem.
This armchair is very comfortable.

comfortable / convenient
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comfortable
Providing a feeling of physical well-being and relaxation; not restrictive or tiring.
Dieser Sessel ist sehr bequem.
This armchair is very comfortable.

The meaning of 'bequem' depends heavily on the context. If it refers to a piece of furniture or clothing, it means 'comfortable'. If it describes an action, it means 'convenient' or 'easy'. If it characterizes a person, it means 'lazy' or 'idle'.
Mein neuer Stuhl ist sehr bequem.
My new chair is very comfortable.
The related noun is 'die Bequemlichkeit' (comfort/convenience/laziness). It describes either the comfort of something or the quality of a person who avoids effort.
Die Bequemlichkeit dieses Sessels ist unübertroffen.
The comfort of this armchair is unmatched.
When referring to physical well-being, 'bequem' (comfortable) is often combined with clothing, shoes, or furniture. A typical phrase is also 'es sich bequem machen' (to make oneself comfortable).
Zieh dir bequeme Schuhe für die Wanderung an.
Put on comfortable shoes for the hike.
In the meaning 'einfach' (easy) or 'mühelos' (effortless), 'bequem' (convenient) is very often used in the structure 'es ist bequem, etwas zu tun' (it is convenient to do something).
Es ist bequem, mit der U-Bahn ins Stadtzentrum zu fahren.
It is convenient to take the subway into the city center.
When 'bequem' describes a person, it often has a slightly negative or critical meaning. It implies that the person avoids effort and tends toward laziness.
Mein Mitbewohner ist zu bequem, um sein Geschirr sofort zu spülen.
My roommate is too lazy to wash his dishes right away.
simple / just
'einfach' and 'bequem' can both express that something takes little effort. 'einfach' mainly means: not complicated, easy to understand, or easy to do. 'bequem' often means: comfortable for the body, for example a chair or shoes. But it can also mean that something can be done without much effort, for example 'eine bequeme Lösung' (a convenient solution). Learners confuse the words because both can sometimes seem like 'easy'. For tasks, rules, or explanations, 'einfach' usually fits. For sitting, clothing, travel, or effortless ways of doing something, 'bequem' often fits.

Nach der langen Fahrt war der breite Sessel besonders bequem.
After the long journey, the wide armchair was especially comfortable.
Die Anleitung ist einfach, deshalb kann ich das Regal allein aufbauen.
The instructions are easy, so I can assemble the shelf by myself.