I would thank you from the bottom of my heart, but for you my heart has no bottom.
Te agradezco desde el fondo de mi corazón, pero para ti, mi corazón no tiene fondo.
Just a note further to your question above about whether the verb following - 'it is likely that' - should be in the subjunctive or not - you may find this link helpful.
Uses of the subjunctive
It says in part, regarding when to use the subjunctive:
Noun clauses may function as the object or predicate compliment of a verb. Remember the importance of governing verbs and their effect on subordinate noun clauses: normally verbs such as reporting, affirmation, knowledge and certainty (think, believe, affirm, be certain of, etc.), are followed by the indicative. In contrast, the subjunctive is used in dependent clauses following: 1) verbs of influence, such as urge, advise, permit, forbid, ask, or want (someone else to do something); 2) verbs of doubt or denial, such as doubt, deny, be unsure of; 3) verbs of emotion such as regret, be happy, be sorry, fear; 4) impersonal expressions indicating these things or subjective reactions, for example, that it is good/bad, (im)possible, (im)probable, (un)likely (that something happen).