command 1

- /summon minecraft:horse ~ ~ ~ {Silent:1b,NoAI:1b,CustomName:"chair",Age:6000,ActiveEffects:[{Id:6b,Amplifier:255b,Duration:999999,ShowParticles:0b},{Id:2b,Amplifier:255b,Duration:999999,ShowParticles:0b},{Id:14b,Amplifier:1b,Duration:999999,ShowParticles:0b}],Attributes:[{AttributeName:"generic.maxHealth",Base:1d,Modifiers:]}],Tame:1,SaddleItem:{id:saddle,Count:1},NoAI:1b,NoGravity:1b}

command 2 - repeating command

- /effect @e[name=chair] minecraft:slowness 1 255 true

command 3 - tp to the right position

- /tp @e[name=chair,c=1] @p
- /tp @e[name=chair,c=1] ~ ~-1.5 ~ (only for Bench)
/tp @e[name=chair,c=1] ~ ~-1.7 ~ (only for office chair)
/tp @e[name=chair,c=1] ~ ~-1.4 ~ (only for modern chair)