Synonyms for comfortable

Most common

1. Easy

2. Comfy — comforting, providing comfort; consolatory

Other

cheerful, sufficient, cheery, domestic

adj. 1
Comforting, providing comfort; consolatory.
adj. 2
Providing physical comfort and ease; agreeable.
This is the most comfortable bed I’ve ever slept in.

Comfortable, Contented, Satisfied, At Ease or At Rest?

A person is comfortable in mind when contented and measurably satisfied. He is comfortable in body when free from pain, quiet, at ease, at rest.

J. C. Fernald, English Synonyms and Antonyms (1914)

satisfied I am by no means satisfied with my present income.
convenient Come and see me whenever it is convenient for you.
commodious I found the suites capacious, the sofas commodious, the sandwiches copious.
cozy The cabin Gustavo constructed was cozy and rustic.
snug I tucked her into bed, as snug as a bug in a rug.

Use in printed books, per decade from 1850 to 2019.

4 letters: easy², safe¹, rich¹, cozy², cosy², snug¹
5 letters: comfy², cushy², rangy²
6 letters: cheery², homely²
7 letters: welcome², restful², eathful
8 letters: domestic³, grateful², pleasant², cheerful², homelike²
9 letters: satisfied³, agreeable⁴, contented³
10 letters: acceptable⁴, sufficient³, convenient³, prosperous³, comforting³, gratifying⁴, commodious⁴
12 letters: satisfactory⁴

The small number after each word is its number of syllables (easy² = 2 syllables).